The Industrial Raspberry Pi Forum

Hi,
I'm trying to make a Modbus RTU connection betwen a PCD3 from SAIA and my Revolution Pi.
I configured the revolution pi as master and the PCD3 as slave (server in the PG5 Software).
Unfortunately I can not read the status of the bit, I only have the value 0 with piTest, even when the bit is set to 1.
Here is my Master configuration:


and here is my configuration in SAIA's PG5 software:




Do you have any idea what I did not do correctly?

Thanks,
Norian




For now I'm just trying to read a bit.

Hi Norian,
please check the following registers "Modbus_Action_Status_x and Modbus_Master_Status.
A description of the error codes can be found here.

I've found with Modbus, one company's idea of Modbus addressing can be quite different from anothers.

I'd start at 0 then try 1 (some companies start at 1, oddly), then try multiples of 10, ie 1000 (or 1001), 10000 (or 10001) until you find an agreement.

Some company's implementation don't support some types or support them wrongly, ie they have "holding registers" as inputs instead of outputs and so on.

Some companies don't support bits at all, just integers (so you have to start at 10000 or 10001 or (older implementations) 1000 or 1001 (or even 100 or 101 if it's very old)).

There's a lot of bad/wrong/misleading implementations - don't expect addressing to be consistent!

Out of interest, how are you connected to the modbus unit?

Modbus RTU is either RS232 or RS485 (Rs485 is either 2 wire or 4 wire), which of these 3 options have you used?

Do you have a serial converter attached to the RevPi core?

Are you sure the slave address (in "Extended data" is correct?