I now have Brains writing a integer from Mach to the holding register of a Micrologix 1200 PLC. I can't understand how it is working though!
According to the manual, the holding register addressing should start at 40001. I set the Address Modbus(Var) in the serial plugin to 40001, with 4 registers and Output-Holding.
The test Modbus worked fine, I was able to read write to these registers.
In Brains is where I struggled to write to the appropriate register through the Modbus output. The information was going somewhere in the PLC, cause I was able to read it back through brains also, but I don't know where it was going.
I was, however, able to write to the correct register by using the Sendstring output. This was not appropriate for sending an integer though.
So anyway, after most of a day, I changed the Address Modbus(Var) to 0 and that solved the problem. I don't understand this though, and that bothers me!
How is it getting to the correct address?

Thanks,
Joe