ESP32 Modbus Server Example

In this project we are using the CAS Modbus stack (https://store.chipkin.com) to generate a simple Modbus TCP server with three registers 40001-40003. Depening on the state of the registers the built in LED wil on/off/blink. A Modbus Client/Master application (such as CAS Modbus Scanner) can be used to read/write to these registers and to change the values.

Register	Description	Default
40001	LED Mode (1 = Off, 2 = On, 3 = Blink)	3
40002	LED Blink Speed in milliseconds	200
40003	LED Current state (0 = OFF, 1 = ON)	0
40004	Running Count. This value incurments once a second and loops every ~18 hours.	0
40005	Spare	0
40006	Spare	0
40007	Spare	0
40008	Spare	0
40009	Spare	0

Quick start

Download and install Platform/io for Visual studios code
Add the ESP32 board to Platform/io
Add the CAS Modbus stack libary to the /lib/ folder.
Use Platform/io to Build the project.
Use Platform/io to Upload and Monitor.

Supported Modbus functions

The CAS Modbus stack supports many other Modbus functions, this minumial example only supports the following:

03 (0x03) Read Holding Registers
06 (0x06) Write Single Register
16 (0x10) Write Multiple registers

Example output from CAS Modbus Scanner

The following output was produced using the CAS Modbus Scanner when reading values from the ESP32-ModbusServerExample.

Poll: FF 03 00 00 00 09
Response: 01 03 12 00 03 00 FA 00 01 90 5A 00 00 00 00 00 00 00 00 00 00

Register	Value (Hex)	Value (Uint16)
40001	0x0003	3
40002	0x00FA	250
40003	0x0001	1
40004	0x905A	36954
40005	0x0000	0
40006	0x0000	0
40007	0x0000	0
40008	0x0000	0
40009	0x0000	0

Example in the CAS Modbus Scanner

Example output

The example output from the serial terminal of the ESP32

FYI: ESP32 CAS Modbus Stack example version: 0.0.1
FYI: ESP32 Chip ID: 30C6, (08A4AE30)
FYI: Connecting to wifi...
FYI: Connected to XXXXXXXXXXXX
FYI: IP address: 192.168.1.66
FYI: Subnet mask: 255.255.255.0
FYI: CAS Modbus Stack version: 2.3.11
FYI: FreeHeap: 280012 / 343144 (81.60 %)
FYI: New TCP connection
FYI: RemoteIP: 192.168.1.77, Port: 27484
FYI: RecvModbusMessage bytes=[12]
FYI: GetModbusValue slaveAddress=[1], function=[3], startingAddress=[0], length=[9]
   40001 = 3 (0x0003)
   40002 = 250 (0x00FA)
   40003 = 1 (0x0001)
   40004 = 36954 (0x905A)
   40005 = 0 (0x0000)
   40006 = 0 (0x0000)
   40007 = 0 (0x0000)
   40008 = 0 (0x0000)
   40009 = 0 (0x0000)
FYI: sendModbusMessage bytes=[27]
FYI: FreeHeap: 277328 / 342900 (80.88 %)
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chipkin/ESP32-ModbusServerExample