diff --git a/components/freemodbus/common/esp_modbus_callbacks.h b/components/freemodbus/common/esp_modbus_callbacks.h
index d9875a6..6bcd15f 100644
--- a/components/freemodbus/common/esp_modbus_callbacks.h
+++ b/components/freemodbus/common/esp_modbus_callbacks.h
@@ -1,17 +1,8 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
-*/
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 // Stack callback functions prototypes
 
diff --git a/components/freemodbus/common/esp_modbus_master.c b/components/freemodbus/common/esp_modbus_master.c
index 2684d0e..8ff474b 100644
--- a/components/freemodbus/common/esp_modbus_master.c
+++ b/components/freemodbus/common/esp_modbus_master.c
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 #include "esp_err.h"            // for esp_err_t
diff --git a/components/freemodbus/common/esp_modbus_master_serial.c b/components/freemodbus/common/esp_modbus_master_serial.c
index 2617974..9ea355b 100644
--- a/components/freemodbus/common/esp_modbus_master_serial.c
+++ b/components/freemodbus/common/esp_modbus_master_serial.c
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 #include "esp_err.h"                // for esp_err_t
diff --git a/components/freemodbus/common/esp_modbus_master_tcp.c b/components/freemodbus/common/esp_modbus_master_tcp.c
index 4bedfe8..8350f73 100644
--- a/components/freemodbus/common/esp_modbus_master_tcp.c
+++ b/components/freemodbus/common/esp_modbus_master_tcp.c
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 #include "esp_err.h"                // for esp_err_t
diff --git a/components/freemodbus/common/esp_modbus_slave.c b/components/freemodbus/common/esp_modbus_slave.c
index f69599c..143cf16 100644
--- a/components/freemodbus/common/esp_modbus_slave.c
+++ b/components/freemodbus/common/esp_modbus_slave.c
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 #include "esp_err.h"                // for esp_err_t
diff --git a/components/freemodbus/common/esp_modbus_slave_serial.c b/components/freemodbus/common/esp_modbus_slave_serial.c
index 89b75f4..eb08dfd 100644
--- a/components/freemodbus/common/esp_modbus_slave_serial.c
+++ b/components/freemodbus/common/esp_modbus_slave_serial.c
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 #include "esp_err.h"                    // for esp_err_t
diff --git a/components/freemodbus/common/esp_modbus_slave_tcp.c b/components/freemodbus/common/esp_modbus_slave_tcp.c
index 2384690..c3b3ee6 100644
--- a/components/freemodbus/common/esp_modbus_slave_tcp.c
+++ b/components/freemodbus/common/esp_modbus_slave_tcp.c
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 #include "esp_err.h"                // for esp_err_t
diff --git a/components/freemodbus/common/include/esp_modbus_common.h b/components/freemodbus/common/include/esp_modbus_common.h
index aa53e85..f624a64 100644
--- a/components/freemodbus/common/include/esp_modbus_common.h
+++ b/components/freemodbus/common/include/esp_modbus_common.h
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 #ifndef _MB_IFACE_COMMON_H
diff --git a/components/freemodbus/common/include/esp_modbus_master.h b/components/freemodbus/common/include/esp_modbus_master.h
index 5d7539b..433e143 100644
--- a/components/freemodbus/common/include/esp_modbus_master.h
+++ b/components/freemodbus/common/include/esp_modbus_master.h
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 #ifndef _ESP_MB_MASTER_INTERFACE_H
diff --git a/components/freemodbus/common/include/esp_modbus_slave.h b/components/freemodbus/common/include/esp_modbus_slave.h
index fa6a53b..13fd456 100644
--- a/components/freemodbus/common/include/esp_modbus_slave.h
+++ b/components/freemodbus/common/include/esp_modbus_slave.h
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 #ifndef _ESP_MB_SLAVE_INTERFACE_H
diff --git a/components/freemodbus/common/include/mbcontroller.h b/components/freemodbus/common/include/mbcontroller.h
index 08b3c18..10205f8 100644
--- a/components/freemodbus/common/include/mbcontroller.h
+++ b/components/freemodbus/common/include/mbcontroller.h
@@ -1,17 +1,8 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
-*/
+ * SPDX-License-Identifier: Apache-2.0
+ */
 //  mbcontroller.h
 //  mbcontroller - common Modbus controller header file
 
diff --git a/components/freemodbus/common/mbc_master.h b/components/freemodbus/common/mbc_master.h
index 67e5f55..f0d0d37 100644
--- a/components/freemodbus/common/mbc_master.h
+++ b/components/freemodbus/common/mbc_master.h
@@ -1,17 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
+
 #ifndef _MB_CONTROLLER_MASTER_H
 #define _MB_CONTROLLER_MASTER_H
 
diff --git a/components/freemodbus/common/mbc_slave.h b/components/freemodbus/common/mbc_slave.h
index a116314..b7dd4bd 100644
--- a/components/freemodbus/common/mbc_slave.h
+++ b/components/freemodbus/common/mbc_slave.h
@@ -1,17 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
+
 #ifndef _MB_CONTROLLER_SLAVE_H
 #define _MB_CONTROLLER_SLAVE_H
 
diff --git a/components/freemodbus/modbus/ascii/mbascii.c b/components/freemodbus/modbus/ascii/mbascii.c
index 132711e..462a641 100644
--- a/components/freemodbus/modbus/ascii/mbascii.c
+++ b/components/freemodbus/modbus/ascii/mbascii.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/ascii/mbascii.h b/components/freemodbus/modbus/ascii/mbascii.h
index 93cc688..e4a2c6a 100644
--- a/components/freemodbus/modbus/ascii/mbascii.h
+++ b/components/freemodbus/modbus/ascii/mbascii.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/ascii/mbascii_m.c b/components/freemodbus/modbus/ascii/mbascii_m.c
index 94c0421..8106598 100644
--- a/components/freemodbus/modbus/ascii/mbascii_m.c
+++ b/components/freemodbus/modbus/ascii/mbascii_m.c
@@ -1,3 +1,8 @@
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/functions/mbfunccoils.c b/components/freemodbus/modbus/functions/mbfunccoils.c
index 40ca1c1..600c756 100644
--- a/components/freemodbus/modbus/functions/mbfunccoils.c
+++ b/components/freemodbus/modbus/functions/mbfunccoils.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/functions/mbfunccoils_m.c b/components/freemodbus/modbus/functions/mbfunccoils_m.c
index 931f536..cbd5e3c 100644
--- a/components/freemodbus/modbus/functions/mbfunccoils_m.c
+++ b/components/freemodbus/modbus/functions/mbfunccoils_m.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (C) 2013 Armink <armink.ztl@gmail.com>
diff --git a/components/freemodbus/modbus/functions/mbfuncdiag.c b/components/freemodbus/modbus/functions/mbfuncdiag.c
index 8f7b967..b988cb8 100644
--- a/components/freemodbus/modbus/functions/mbfuncdiag.c
+++ b/components/freemodbus/modbus/functions/mbfuncdiag.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/functions/mbfuncdisc.c b/components/freemodbus/modbus/functions/mbfuncdisc.c
index 79ff68f..1c022e4 100644
--- a/components/freemodbus/modbus/functions/mbfuncdisc.c
+++ b/components/freemodbus/modbus/functions/mbfuncdisc.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: LGPL-2.0-only
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
  /*
   * FreeRTOS Modbus Libary: A Modbus serial implementation for FreeRTOS
   * Copyright (C) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/functions/mbfuncdisc_m.c b/components/freemodbus/modbus/functions/mbfuncdisc_m.c
index 21ce0cb..3a079ba 100644
--- a/components/freemodbus/modbus/functions/mbfuncdisc_m.c
+++ b/components/freemodbus/modbus/functions/mbfuncdisc_m.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (C) 2013 Armink <armink.ztl@gmail.com>
@@ -28,8 +35,6 @@
  * File: $Id: mbfuncdisc_m.c,v 1.60 2013/10/15 8:48:20 Armink Add Master Functions  Exp $
  */
 
-
-
 /* ----------------------- System includes ----------------------------------*/
 #include "stdlib.h"
 #include "string.h"
diff --git a/components/freemodbus/modbus/functions/mbfuncholding.c b/components/freemodbus/modbus/functions/mbfuncholding.c
index 6038738..723ba1a 100644
--- a/components/freemodbus/modbus/functions/mbfuncholding.c
+++ b/components/freemodbus/modbus/functions/mbfuncholding.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/functions/mbfuncholding_m.c b/components/freemodbus/modbus/functions/mbfuncholding_m.c
index 9c3d699..48b7c7b 100644
--- a/components/freemodbus/modbus/functions/mbfuncholding_m.c
+++ b/components/freemodbus/modbus/functions/mbfuncholding_m.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (C) 2013 Armink <armink.ztl@gmail.com>
diff --git a/components/freemodbus/modbus/functions/mbfuncinput.c b/components/freemodbus/modbus/functions/mbfuncinput.c
index b713d86..2880bd9 100644
--- a/components/freemodbus/modbus/functions/mbfuncinput.c
+++ b/components/freemodbus/modbus/functions/mbfuncinput.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/functions/mbfuncinput_m.c b/components/freemodbus/modbus/functions/mbfuncinput_m.c
index 37135f7..2db16d6 100644
--- a/components/freemodbus/modbus/functions/mbfuncinput_m.c
+++ b/components/freemodbus/modbus/functions/mbfuncinput_m.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (C) 2013 Armink <armink.ztl@gmail.com>
diff --git a/components/freemodbus/modbus/functions/mbfuncother.c b/components/freemodbus/modbus/functions/mbfuncother.c
index 0c2323a..59d6bda 100644
--- a/components/freemodbus/modbus/functions/mbfuncother.c
+++ b/components/freemodbus/modbus/functions/mbfuncother.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/functions/mbutils.c b/components/freemodbus/modbus/functions/mbutils.c
index 0f0928b..1332c02 100644
--- a/components/freemodbus/modbus/functions/mbutils.c
+++ b/components/freemodbus/modbus/functions/mbutils.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/include/mb.h b/components/freemodbus/modbus/include/mb.h
index bd0f24a..964e3e1 100644
--- a/components/freemodbus/modbus/include/mb.h
+++ b/components/freemodbus/modbus/include/mb.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/include/mb_m.h b/components/freemodbus/modbus/include/mb_m.h
index cb088e9..4eb7723 100644
--- a/components/freemodbus/modbus/include/mb_m.h
+++ b/components/freemodbus/modbus/include/mb_m.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (C) 2013 Armink <armink.ztl@gmail.com>
diff --git a/components/freemodbus/modbus/include/mbconfig.h b/components/freemodbus/modbus/include/mbconfig.h
index b029786..897cc6c 100644
--- a/components/freemodbus/modbus/include/mbconfig.h
+++ b/components/freemodbus/modbus/include/mbconfig.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/include/mbframe.h b/components/freemodbus/modbus/include/mbframe.h
index 5b7d6d7..6e6abac 100644
--- a/components/freemodbus/modbus/include/mbframe.h
+++ b/components/freemodbus/modbus/include/mbframe.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/include/mbfunc.h b/components/freemodbus/modbus/include/mbfunc.h
index 48d7b39..fcb88bb 100644
--- a/components/freemodbus/modbus/include/mbfunc.h
+++ b/components/freemodbus/modbus/include/mbfunc.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/include/mbport.h b/components/freemodbus/modbus/include/mbport.h
index a73b949..146973e 100644
--- a/components/freemodbus/modbus/include/mbport.h
+++ b/components/freemodbus/modbus/include/mbport.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/include/mbproto.h b/components/freemodbus/modbus/include/mbproto.h
index 3c76517..da303a6 100644
--- a/components/freemodbus/modbus/include/mbproto.h
+++ b/components/freemodbus/modbus/include/mbproto.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/include/mbutils.h b/components/freemodbus/modbus/include/mbutils.h
index 1d96ddc..de64c4a 100644
--- a/components/freemodbus/modbus/include/mbutils.h
+++ b/components/freemodbus/modbus/include/mbutils.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/mb.c b/components/freemodbus/modbus/mb.c
index 2572201..60ba538 100644
--- a/components/freemodbus/modbus/mb.c
+++ b/components/freemodbus/modbus/mb.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/mb_m.c b/components/freemodbus/modbus/mb_m.c
index f23a577..aa5922a 100644
--- a/components/freemodbus/modbus/mb_m.c
+++ b/components/freemodbus/modbus/mb_m.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (C) 2013 Armink <armink.ztl@gmail.com>
diff --git a/components/freemodbus/modbus/rtu/mbcrc.c b/components/freemodbus/modbus/rtu/mbcrc.c
index bb89676..c46e7d1 100644
--- a/components/freemodbus/modbus/rtu/mbcrc.c
+++ b/components/freemodbus/modbus/rtu/mbcrc.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/rtu/mbcrc.h b/components/freemodbus/modbus/rtu/mbcrc.h
index 5ed3f22..d74d9eb 100644
--- a/components/freemodbus/modbus/rtu/mbcrc.h
+++ b/components/freemodbus/modbus/rtu/mbcrc.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/rtu/mbrtu.c b/components/freemodbus/modbus/rtu/mbrtu.c
index c4d77f6..180bde2 100644
--- a/components/freemodbus/modbus/rtu/mbrtu.c
+++ b/components/freemodbus/modbus/rtu/mbrtu.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/rtu/mbrtu.h b/components/freemodbus/modbus/rtu/mbrtu.h
index 676f67d..69e0f45 100644
--- a/components/freemodbus/modbus/rtu/mbrtu.h
+++ b/components/freemodbus/modbus/rtu/mbrtu.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/rtu/mbrtu_m.c b/components/freemodbus/modbus/rtu/mbrtu_m.c
index ce22c8e..47a5513 100644
--- a/components/freemodbus/modbus/rtu/mbrtu_m.c
+++ b/components/freemodbus/modbus/rtu/mbrtu_m.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2013 China Beijing Armink <armink.ztl@gmail.com>
diff --git a/components/freemodbus/modbus/tcp/mbtcp.c b/components/freemodbus/modbus/tcp/mbtcp.c
index 2527752..9612d57 100644
--- a/components/freemodbus/modbus/tcp/mbtcp.c
+++ b/components/freemodbus/modbus/tcp/mbtcp.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/tcp/mbtcp.h b/components/freemodbus/modbus/tcp/mbtcp.h
index 89e970a..842ce19 100644
--- a/components/freemodbus/modbus/tcp/mbtcp.h
+++ b/components/freemodbus/modbus/tcp/mbtcp.h
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/tcp/mbtcp_m.c b/components/freemodbus/modbus/tcp/mbtcp_m.c
index 05eca0d..6a282b6 100644
--- a/components/freemodbus/modbus/tcp/mbtcp_m.c
+++ b/components/freemodbus/modbus/tcp/mbtcp_m.c
@@ -1,3 +1,10 @@
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/modbus/tcp/mbtcp_m.h b/components/freemodbus/modbus/tcp/mbtcp_m.h
index 34aaa02..901cd0e 100644
--- a/components/freemodbus/modbus/tcp/mbtcp_m.h
+++ b/components/freemodbus/modbus/tcp/mbtcp_m.h
@@ -1,3 +1,8 @@
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 /*
  * FreeModbus Libary: A portable Modbus implementation for Modbus ASCII/RTU.
  * Copyright (c) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/port/port.c b/components/freemodbus/port/port.c
index dd9063f..9659bd5 100644
--- a/components/freemodbus/port/port.c
+++ b/components/freemodbus/port/port.c
@@ -1,16 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: LGPL-2.0-only
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
   * FreeModbus Libary: RT-Thread Port
diff --git a/components/freemodbus/port/port.h b/components/freemodbus/port/port.h
index e67f56c..f82e497 100644
--- a/components/freemodbus/port/port.h
+++ b/components/freemodbus/port/port.h
@@ -1,16 +1,38 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2010 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: BSD-3-Clause
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
+/*
+ * FreeModbus Libary: ESP32 Port Demo Application
+ * Copyright (C) 2010 Christian Walter <cwalter@embedded-solutions.at>
  *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * IF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * File: $Id: portother.c,v 1.1 2010/06/06 13:07:20 wolti Exp $
  */
 
 #ifndef PORT_COMMON_H_
diff --git a/components/freemodbus/port/portevent.c b/components/freemodbus/port/portevent.c
index 20e2bce..adb5865 100644
--- a/components/freemodbus/port/portevent.c
+++ b/components/freemodbus/port/portevent.c
@@ -1,16 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2010 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: BSD-3-Clause
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Port Demo Application
diff --git a/components/freemodbus/port/portevent_m.c b/components/freemodbus/port/portevent_m.c
index 21975bc..b9d97be 100644
--- a/components/freemodbus/port/portevent_m.c
+++ b/components/freemodbus/port/portevent_m.c
@@ -1,16 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: LGPL-2.0-only
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Port Demo Application
diff --git a/components/freemodbus/port/portother.c b/components/freemodbus/port/portother.c
index 0ff251c..180de5b 100644
--- a/components/freemodbus/port/portother.c
+++ b/components/freemodbus/port/portother.c
@@ -1,16 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2010 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: BSD-3-Clause
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Demo Application
diff --git a/components/freemodbus/port/portother_m.c b/components/freemodbus/port/portother_m.c
index bdc471c..fa2d421 100644
--- a/components/freemodbus/port/portother_m.c
+++ b/components/freemodbus/port/portother_m.c
@@ -1,16 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: BSD-3-Clause
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Demo Application
diff --git a/components/freemodbus/port/portserial.c b/components/freemodbus/port/portserial.c
index f860995..2d4b80c 100644
--- a/components/freemodbus/port/portserial.c
+++ b/components/freemodbus/port/portserial.c
@@ -1,16 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2010 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: BSD-3-Clause
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Port Demo Application
diff --git a/components/freemodbus/port/portserial_m.c b/components/freemodbus/port/portserial_m.c
index 71ea9a8..6bf1623 100644
--- a/components/freemodbus/port/portserial_m.c
+++ b/components/freemodbus/port/portserial_m.c
@@ -1,16 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2013 Armink
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: LGPL-2.0-only
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Port Demo Application
diff --git a/components/freemodbus/port/porttimer.c b/components/freemodbus/port/porttimer.c
index 7497b6d..64c17a9 100644
--- a/components/freemodbus/port/porttimer.c
+++ b/components/freemodbus/port/porttimer.c
@@ -1,7 +1,9 @@
 /*
- * SPDX-FileCopyrightText: 2018-2021 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2010 Christian Walter
  *
- * SPDX-License-Identifier: Apache-2.0
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Port Demo Application
diff --git a/components/freemodbus/port/porttimer_m.c b/components/freemodbus/port/porttimer_m.c
index 756b52a..591a361 100644
--- a/components/freemodbus/port/porttimer_m.c
+++ b/components/freemodbus/port/porttimer_m.c
@@ -1,7 +1,9 @@
 /*
- * SPDX-FileCopyrightText: 2018-2021 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2013 Armink
  *
- * SPDX-License-Identifier: Apache-2.0
+ * SPDX-License-Identifier: LGPL-2.0-only
+ *
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Port Demo Application
diff --git a/components/freemodbus/serial_master/modbus_controller/mbc_serial_master.c b/components/freemodbus/serial_master/modbus_controller/mbc_serial_master.c
index ebd38ee..a41e572 100644
--- a/components/freemodbus/serial_master/modbus_controller/mbc_serial_master.c
+++ b/components/freemodbus/serial_master/modbus_controller/mbc_serial_master.c
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 // mbc_serial_master.c
diff --git a/components/freemodbus/serial_master/modbus_controller/mbc_serial_master.h b/components/freemodbus/serial_master/modbus_controller/mbc_serial_master.h
index 5ed72c9..28aec53 100644
--- a/components/freemodbus/serial_master/modbus_controller/mbc_serial_master.h
+++ b/components/freemodbus/serial_master/modbus_controller/mbc_serial_master.h
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 //  mbc_serial_master.h Modbus controller serial master implementation header file
diff --git a/components/freemodbus/serial_master/port/port_serial_master.h b/components/freemodbus/serial_master/port/port_serial_master.h
index c639743..bc74966 100644
--- a/components/freemodbus/serial_master/port/port_serial_master.h
+++ b/components/freemodbus/serial_master/port/port_serial_master.h
@@ -1,16 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2010 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: BSD-3-Clause
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Port Demo Application
diff --git a/components/freemodbus/serial_slave/modbus_controller/mbc_serial_slave.c b/components/freemodbus/serial_slave/modbus_controller/mbc_serial_slave.c
index b45e839..4f3dfaf 100644
--- a/components/freemodbus/serial_slave/modbus_controller/mbc_serial_slave.c
+++ b/components/freemodbus/serial_slave/modbus_controller/mbc_serial_slave.c
@@ -1,18 +1,8 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
-
 // mbc_serial_slave.c
 // Implementation of the Modbus controller serial slave
 
diff --git a/components/freemodbus/serial_slave/modbus_controller/mbc_serial_slave.h b/components/freemodbus/serial_slave/modbus_controller/mbc_serial_slave.h
index e8c5c3d..9a515ba 100644
--- a/components/freemodbus/serial_slave/modbus_controller/mbc_serial_slave.h
+++ b/components/freemodbus/serial_slave/modbus_controller/mbc_serial_slave.h
@@ -1,16 +1,7 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 //  mbc_serial_slave.h Modbus controller serial slave implementation header file
diff --git a/components/freemodbus/serial_slave/port/port_serial_slave.h b/components/freemodbus/serial_slave/port/port_serial_slave.h
index 16d299c..26c13cd 100644
--- a/components/freemodbus/serial_slave/port/port_serial_slave.h
+++ b/components/freemodbus/serial_slave/port/port_serial_slave.h
@@ -1,16 +1,9 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2010 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: BSD-3-Clause
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
  */
 /*
  * FreeModbus Libary: ESP32 Port Demo Application
diff --git a/components/freemodbus/tcp_master/modbus_controller/mbc_tcp_master.h b/components/freemodbus/tcp_master/modbus_controller/mbc_tcp_master.h
index 9593f77..b0731df 100644
--- a/components/freemodbus/tcp_master/modbus_controller/mbc_tcp_master.h
+++ b/components/freemodbus/tcp_master/modbus_controller/mbc_tcp_master.h
@@ -1,17 +1,8 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
-*/
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 //  mbc_tcp_master.h Modbus controller TCP master implementation header file
 
diff --git a/components/freemodbus/tcp_master/port/port_tcp_master.c b/components/freemodbus/tcp_master/port/port_tcp_master.c
index f4ace75..2c99c9a 100644
--- a/components/freemodbus/tcp_master/port/port_tcp_master.c
+++ b/components/freemodbus/tcp_master/port/port_tcp_master.c
@@ -1,17 +1,10 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: LGPL-2.0-only
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
-*/
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
   * FreeModbus Libary: ESP32 TCP Port
   * Copyright (C) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/tcp_master/port/port_tcp_master.h b/components/freemodbus/tcp_master/port/port_tcp_master.h
index c6a72fb..f49f8bc 100644
--- a/components/freemodbus/tcp_master/port/port_tcp_master.h
+++ b/components/freemodbus/tcp_master/port/port_tcp_master.h
@@ -1,17 +1,10 @@
- /* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: LGPL-2.0-only
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
-*/
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
  /*
   * FreeModbus Libary: ESP32 TCP Port
   * Copyright (C) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/tcp_slave/modbus_controller/mbc_tcp_slave.c b/components/freemodbus/tcp_slave/modbus_controller/mbc_tcp_slave.c
index e02a24a..240a69f 100644
--- a/components/freemodbus/tcp_slave/modbus_controller/mbc_tcp_slave.c
+++ b/components/freemodbus/tcp_slave/modbus_controller/mbc_tcp_slave.c
@@ -1,17 +1,8 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
-*/
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 // mbc_tcp_slave.c
 // Implementation of the Modbus controller TCP slave
diff --git a/components/freemodbus/tcp_slave/modbus_controller/mbc_tcp_slave.h b/components/freemodbus/tcp_slave/modbus_controller/mbc_tcp_slave.h
index 0987610..56ece0d 100644
--- a/components/freemodbus/tcp_slave/modbus_controller/mbc_tcp_slave.h
+++ b/components/freemodbus/tcp_slave/modbus_controller/mbc_tcp_slave.h
@@ -1,17 +1,8 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
-*/
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 //  mbc_tcp_slave.h Modbus controller TCP slave implementation header file
 
diff --git a/components/freemodbus/tcp_slave/port/port_tcp_slave.c b/components/freemodbus/tcp_slave/port/port_tcp_slave.c
index 3c4df63..473c802 100644
--- a/components/freemodbus/tcp_slave/port/port_tcp_slave.c
+++ b/components/freemodbus/tcp_slave/port/port_tcp_slave.c
@@ -1,17 +1,10 @@
-/* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: LGPL-2.0-only
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
-*/
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
 /*
   * FreeModbus Libary: ESP32 TCP Port
   * Copyright (C) 2006 Christian Walter <wolti@sil.at>
diff --git a/components/freemodbus/tcp_slave/port/port_tcp_slave.h b/components/freemodbus/tcp_slave/port/port_tcp_slave.h
index ffed795..d71f8b9 100644
--- a/components/freemodbus/tcp_slave/port/port_tcp_slave.h
+++ b/components/freemodbus/tcp_slave/port/port_tcp_slave.h
@@ -1,17 +1,10 @@
- /* Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+/*
+ * SPDX-FileCopyrightText: 2006 Christian Walter
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * SPDX-License-Identifier: LGPL-2.0-only
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
-*/
+ * SPDX-FileContributor: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ */
  /*
   * FreeModbus Libary: ESP32 TCP Port
   * Copyright (C) 2006 Christian Walter <wolti@sil.at>
diff --git a/examples/protocols/modbus/mb_example_common/modbus_params.c b/examples/protocols/modbus/mb_example_common/modbus_params.c
index ab31ba4..8a5bbd4 100644
--- a/examples/protocols/modbus/mb_example_common/modbus_params.c
+++ b/examples/protocols/modbus/mb_example_common/modbus_params.c
@@ -1,3 +1,8 @@
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 /*=====================================================================================
  * Description:
  *   C file to define parameter storage instances
diff --git a/examples/protocols/modbus/serial/example_test.py b/examples/protocols/modbus/serial/example_test.py
index c150182..469c1f7 100644
--- a/examples/protocols/modbus/serial/example_test.py
+++ b/examples/protocols/modbus/serial/example_test.py
@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
+# SPDX-License-Identifier: Apache-2.0
+
 # Need Python 3 string formatting functions
 from __future__ import print_function
 
@@ -283,6 +286,5 @@ if __name__ == '__main__':
     logger.addHandler(fh)
     logger.addHandler(ch)
     logger.info('Start script %s.' % os.path.basename(__file__))
-    print('Logging file name: %s' % logger.handlers[0].baseFilename)
     test_modbus_communication()
     logging.shutdown()
diff --git a/examples/protocols/modbus/serial/mb_master/main/master.c b/examples/protocols/modbus/serial/mb_master/main/master.c
index 6b71a57..d7a5f0c 100644
--- a/examples/protocols/modbus/serial/mb_master/main/master.c
+++ b/examples/protocols/modbus/serial/mb_master/main/master.c
@@ -1,16 +1,8 @@
-// Copyright 2016-2019 Espressif Systems (Shanghai) PTE LTD
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 #include "string.h"
 #include "esp_log.h"
diff --git a/examples/protocols/modbus/serial/mb_slave/main/slave.c b/examples/protocols/modbus/serial/mb_slave/main/slave.c
index 30f3a38..da9c249 100644
--- a/examples/protocols/modbus/serial/mb_slave/main/slave.c
+++ b/examples/protocols/modbus/serial/mb_slave/main/slave.c
@@ -1,9 +1,11 @@
-/* FreeModbus Slave Example ESP32
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// FreeModbus Slave Example ESP32
 
-   Unless required by applicable law or agreed to in writing, this
-   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
-   CONDITIONS OF ANY KIND, either express or implied.
-*/
 #include <stdio.h>
 #include <stdint.h>
 #include "esp_err.h"
diff --git a/examples/protocols/modbus/tcp/example_test.py b/examples/protocols/modbus/tcp/example_test.py
index 17c8226..c181f5b 100644
--- a/examples/protocols/modbus/tcp/example_test.py
+++ b/examples/protocols/modbus/tcp/example_test.py
@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
+# SPDX-License-Identifier: Apache-2.0
+
 import logging
 import os
 import re
diff --git a/examples/protocols/modbus/tcp/mb_tcp_master/main/tcp_master.c b/examples/protocols/modbus/tcp/mb_tcp_master/main/tcp_master.c
index 8510013..e2bd6e1 100644
--- a/examples/protocols/modbus/tcp/mb_tcp_master/main/tcp_master.c
+++ b/examples/protocols/modbus/tcp/mb_tcp_master/main/tcp_master.c
@@ -1,16 +1,10 @@
-// Copyright 2016-2019 Espressif Systems (Shanghai) PTE LTD
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// FreeModbus Master Example ESP32
 
 #include "string.h"
 #include "esp_log.h"
diff --git a/examples/protocols/modbus/tcp/mb_tcp_slave/main/tcp_slave.c b/examples/protocols/modbus/tcp/mb_tcp_slave/main/tcp_slave.c
index 3511cfa..f8a920c 100644
--- a/examples/protocols/modbus/tcp/mb_tcp_slave/main/tcp_slave.c
+++ b/examples/protocols/modbus/tcp/mb_tcp_slave/main/tcp_slave.c
@@ -1,9 +1,11 @@
-/* FreeModbus Slave Example ESP32
+/*
+ * SPDX-FileCopyrightText: 2016-2021 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// FreeModbus Slave Example ESP32
 
-   Unless required by applicable law or agreed to in writing, this
-   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
-   CONDITIONS OF ANY KIND, either express or implied.
-*/
 #include <stdio.h>
 #include "esp_err.h"
 #include "sdkconfig.h"