The Industrial Raspberry Pi Forum

I am trying to run a MODBUS Master from my PC that is connected to the Gateway Module. DR = 3, FR = 3 and MD = 0. I can connect sucessfully to the port but when I send modbus commands the messages timeout ? I have RX connected to pin 3, GND to pin 4 and TX to pin 5. The RevPi is connected to the gateway and at some point the PWR light on the gateway module flashes. I am trying to find the cause of this so I want to connect a Modbus master to the gateway module and read and set the 4096 resgister.

Hi Leylan, your configuration means
DR = 3 : 9600 kBit/s
FR = 3 : Even Parity 8 Bit 2 Stop-Bit
MD = 0 : RS-232Mode (V.24 ) +- 10V to Ground Rx/Tx

The pinning for RS232 from the user manual: So your connections alr looking perfect.

I have
RX connected to pin 3,
GND to pin 4 and
TX to pin 5.

What happens in case you use a USB-RS232 interface with QModbusMaster?
Could you use an Oscilloscope?

In the user manual the register 4096 is used for restarting the device.
So the registers for input and output data are as follows: I hope that I could clarify the things here a bit.

Which RevPi Module are you using?

The RevPi works as follows - you configure the module in PiCtory.
Then you can write to the Input and Output data.
I.e. the command "piTest -w Output_1,123" writes 123 to the register 1 of the Modbus-RTU slave so the Master can read register 1 and receives the value 123.