Originally written by Viacheslav Kaloshin and now adapted for STM32 CMSIS-RTOS2 and using UART interrupt directly. Updated to support more than 256 addresses. Supports only Modbus commands Function 3 (Read Holding Registers), Function 6 (Write Single Register) and Function 16 (Write Multiple Registers).
- You need to define your ACTIVE_UART_HANDLE and ACTIVE_UART_INSTANCE in main.h
- You need to enable NVIC global interrupt for the UART port in CubeMX.
- You need to enable the UART RX interrupt at the init phase as "HAL_UART_Receive_IT(&ACTIVE_UART_HANDLE, &rxData, 1);" and define a "uint8_t rxData;" in main.c
To test, I recommend OpenModscan (https://github.com/sanny32/OpenModScan)
Why I write my own implementation?
- It does not need any timers.
- It need only one thread on normal (or the same with interface) priority.
- It can be easy adopted for USB/usart/whatever interfaces.
- It is for fun of course!
- Grab modbus.c and modbus.h to your project
- Fix values in modbus.h for you.
- Call init functions and set slave address
ModBus_Init();
ModBus_SetAddress(1);
- Handle incoming bytes to ModBusInHandle queue (example from USB-CDC)
USBD_CDC_ReceivePacket(&hUsbDeviceFS);
...
for(int i=0;i<(*Len);i++)
{
osMessagePut(ModBusInHandle,Buf[i],0);
}
...
return (USBD_OK);
- Handle outgoing bytes the same way, but from ModBusOutHandle queue
uint8_t buf[256]; // buffer, where we collect output data
uint8_t c = 0; // counter for buffer fill
for(;;)
{
osEvent evt = osMessageGet(ModBusOutHandle,200); // wait here 200 tick
if (evt.status == osEventMessage)
{
buf[c++]=(uint8_t) evt.value.v;
}
if (evt.status == osEventTimeout)
{
if( (c > 0) && (c < 254) ) // ok, something in buffer exist, lets send it
{
CDC_Transmit_FS(&buf[0], c); // by USB-CDC
}
c=0;
}
- In other part code, call ModBus_GetRegister & ModBus_SetRegister for reading & setting register
count = ModBus_GetRegister(0);
ModBus_SetRegister(0,count+1);
I prefer to use ModPoll (http://www.modbusdriver.com/modpoll.html)
So in my case all look like this. Here register 0 & 1 overwritten inside programm for test, and modbus slave on COM5
C:\Users\multi\Downloads\modpoll.3.4\win32>modpoll.exe -a 1 -r 1 -c 5 COM5 100 200 310 400 500
modpoll 3.4 - FieldTalk(tm) Modbus(R) Master Simulator
Copyright (c) 2002-2013 proconX Pty Ltd
Visit http://www.modbusdriver.com for Modbus libraries and tools.
Protocol configuration: Modbus RTU
Slave configuration...: address = 1, start reference = 1, count = 5
Communication.........: COM5, 19200, 8, 1, even, t/o 1.00 s, poll rate 1000 ms
Data type.............: 16-bit register, output (holding) register table
Written 5 references.
C:\Users\multi\Downloads\modpoll.3.4\win32>modpoll.exe -a 1 -r 1 -c 6 COM5
modpoll 3.4 - FieldTalk(tm) Modbus(R) Master Simulator
Copyright (c) 2002-2013 proconX Pty Ltd
Visit http://www.modbusdriver.com for Modbus libraries and tools.
Protocol configuration: Modbus RTU
Slave configuration...: address = 1, start reference = 1, count = 6
Communication.........: COM5, 19200, 8, 1, even, t/o 1.00 s, poll rate 1000 ms
Data type.............: 16-bit register, output (holding) register table
-- Polling slave... (Ctrl-C to stop)
[1]: 118
[2]: 0
[3]: 310
[4]: 400
[5]: 500
[6]: 0
-- Polling slave... (Ctrl-C to stop)
[1]: 140
[2]: 0
[3]: 310
[4]: 400
[5]: 500
[6]: 0
-- Polling slave... (Ctrl-C to stop)
In modbustest directory you find full working example.
I use:
- STM32F3-Discovery board
- Keil uVision 5.22
- STM32CubeMX
#Have fun!#