diff --git a/components/freemodbus/README.rst b/components/freemodbus/README.rst
new file mode 100644
index 0000000000..0c9d8f41b7
--- /dev/null
+++ b/components/freemodbus/README.rst
@@ -0,0 +1,6 @@
+# Modbus assumptions, dependencies and constraints
+
+1. Current implementation of Modbus has limitation: maximum frame size should be less than 120 bytes (default UART receive FIFO full threshold value).
+This limitation is removed in ESP-IDF v4.2.
+
+2. The only one instance of Modbus port can be initialized at the same time.
diff --git a/docs/en/api-reference/protocols/modbus.rst b/docs/en/api-reference/protocols/modbus.rst
index 7e6bc9494d..4131422c28 100644
--- a/docs/en/api-reference/protocols/modbus.rst
+++ b/docs/en/api-reference/protocols/modbus.rst
@@ -109,3 +109,10 @@ The examples below use the FreeModbus library port for serial slave and master i
 
 Please refer to the specific example README.md for details.
 
+Modbus Readme File
+------------------
+
+
+.. include:: ../../../../components/freemodbus/README.rst
+
+
diff --git a/examples/protocols/modbus/serial/README.md b/examples/protocols/modbus/serial/README.md
index 2e5d0b7fc8..a1e2b5ef26 100644
--- a/examples/protocols/modbus/serial/README.md
+++ b/examples/protocols/modbus/serial/README.md
@@ -78,5 +78,7 @@ Kconfig value CONFIG_FMB_MASTER_TIMEOUT_MS_RESPOND (CONFIG_FMB_SERIAL_ASCII_TIME
 ESP_ERR_NOT_SUPPORTED (0x106), ESP_ERR_INVALID_RESPONSE (0x108) - Modbus slave device does not support requested command or register and sent exeption response. 
 
 ESP_ERR_INVALID_STATE (0x103) - Modbus stack is not configured correctly or can't work correctly due to critical failure.
- 
 
+Note: Refer to file below for more information about current implementation of Modbus:
+
+* `components/freemodbus/README.rst`
\ No newline at end of file
diff --git a/examples/protocols/modbus/serial/mb_master/README.md b/examples/protocols/modbus/serial/mb_master/README.md
index 5968f4115b..6132676d58 100644
--- a/examples/protocols/modbus/serial/mb_master/README.md
+++ b/examples/protocols/modbus/serial/mb_master/README.md
@@ -148,3 +148,7 @@ I (10175) MASTER_TEST: Destroy master...
 ```
 The example reads the characteristics from slave device(s), while alarm is not triggered in the slave device (See the "Example parameters definition"). The output line describes Timestamp, Cid of characteristic, Characteristic name (Units), Characteristic value (Hex).
 
+Note: Refer to file below for more information about current implementation of Modbus:
+
+* `components/freemodbus/README.rst`
+
diff --git a/examples/protocols/modbus/serial/mb_slave/README.md b/examples/protocols/modbus/serial/mb_slave/README.md
index 8d09f1ad5d..ddcf658a6c 100644
--- a/examples/protocols/modbus/serial/mb_slave/README.md
+++ b/examples/protocols/modbus/serial/mb_slave/README.md
@@ -89,3 +89,6 @@ I (14001) SLAVE_TEST: Modbus controller destroyed.
 ```
 The output lines describe type of operation, its timestamp, modbus address, access type, storage address in parameter structure and number of registers accordingly.
 
+Note: Refer to file below for more information about current implementation of Modbus:
+
+* `components/freemodbus/README.rst`