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

1. Download and install Platform/io for Visual studios code
2. Add the ESP32 board to Platform/io
3. Add the CAS Modbus stack libary to the /lib/ folder.
4. Use Platform/io to Build the project.
5. 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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Tested hardware

• Adafruit HUZZAH32 – ESP32 Feather Board

FAQ

Can't build the project. CASModbusAdapter.h: No such file or directory

Please see this issue CASBACnetStackAdapter.h: No such file or directory