ModBus IO

A ModBus Client running on a STM32 Nucleo Board featuring follwing IOs:

• Encoder interface
• 4 Analog Inputs
• 10 Digital Outputs
• 16 Digital inputs

Default configuration

The addresses can be defined in common/modbus.h.

Device ID: 1 Baud rate:. 115200, 8N1

Read holding/read input register

Addr	IO
0	Analog in 1
1	Analog in 2
2	Analog in 3
3	Analog in 4
4	Encoder high
5	Encoder low

Configuration holding register

Addr	IO
10	Number of averages for ADC
11	Button pulse length

Coils

Addr
0 - 15	GPIO inputs (read only)
16 - 31	GPIO inputs inverted (read only)
32 - 47	Button inputs with pull-ups (read only) *
100 - 109	GPIO outputs

*Extended button logic:

1. A button is read as 1 when pressed.
2. The buttons are software debounced.
3. A button press events generates a pulse of 100 ms (can be changed with write holding 11) if the button is pressed shorter than that.

This is useful to reduce the ModBus poll rate.

Testing

Read/write registers/coils via python

1. Install https://github.com/favalex/modbus-cli by: pip install modbus_cli
2. Read holding regs and coils in combination with watch:
   watch -n 0.1 modbus /dev/ttyUSB0 -b 115200 -s 1 h@2 3 4 5 c@0 c@1 c@2
3. Write values:
   modbus /dev/ttyUSB0 -b 115200 -s 1 c@0=1
modbus /dev/ttyUSB0 -b 115200 -s 1 h@10=200

Using modpoll

Run one of the examples scripts in modpoll/ :

read_coils.ah
read_holding.sh

Using a C program using libmodbus

See libmodbus_client/

Development

Generate Code

The STM32 drivers are included in this project to ensure version compatibility. But I didn't find a way in CubeMX to set the driver paths correctly. So when generating code from CubeMX, the changes in following files need to be discarded:

stm32f3xx_it.C
.cxproject
.mxproject
.project

(Unless if you make bigger changes, then you need to check them manually)