Communicate PM573-ETH PLC with PSTX Softstarter over Modbus RS485
I'm having trouble communicating an ABB PSTX Softstarter to an ABB PM573-ETH PLC over Modbus RS485. To start, I'll a list of the hardware I'm using:
-ABB PM573-ETH PLC
-ABB TB511 Terminal Base (I've made sure it's not an outdated version)
-ABB PSTX85-600-70 Softstarter
Conections have been made in the following manner (image1):
I've not used 120 ohms end resistors due to not having them at hand at the moment. However, I'd think I don't need them since my wiring is less than 2 feet, baud rate is set to 9600, and I'm trying a simple master-slave arrangement.
On the software side I'm using Automation Builder v1.2 and CoDeSys v188.8.131.52
Here's what I've done in Automation Builder (image2)
And here's what I'm doing in CoDeSys (image3). For the moment, I only want to read registers. Later on, I'll want to write)
On the PLC's display I can see a dot flashing besides "COM1". I assume this means Modbus configuration is done well. But maybe I'm wrong.
On the Softstarter, I'm getting an error: P1E00. Which, according to manual, means Fieldbus communication failure. These are the settings of communication parameters on the PSTX:
12.01 = Modbus RTU slave
12.02 = Modbus RTU
12.03 = On
12.04 = 11
12.09 = 9600
12.10 = Even parity
12.11 = 1 Stop bit
All other parameters of this section haven't been modified. I should also mention that I only have energized the control of the PSTX, I have no 3-phase power connected to it, nor a motor. But I am not receiving any other error message besides the one mentioned before.
When doing a login on CoDeSys, I get a constant error on the COM_MOD_MAST block, "8211dec". Which, according the CoDeSys's help, is the timeout error. This makes sense, since I'm not getting any reading on the array of words I've assigned to the DATA input of the COM_MOD_MAST. The error I get on the PSTX confirms that there's something wrong on the Modbus network.
At the moment I have no idea of what I'm missing in the program's configuration, or if my mistake is somewhere else.
I know I've detailed a lot of information here but it's to make it easier anyone who can to help me out.
Thanks a lot in advance!
Looking on your connection diagram, I could recommend to try disconnecting of term. 1 and 4 from COM1 of PM573.
Actually these are pull-up/pull-down resistors. In case you use them, for sure you have to connect external 120 ohms term. resistor
Try to connect directly term. 2 (RxD/TxD-P) and 3 (Rxd/TxD-N) of COM1 to COM3 port of the softstarter. I'm not quite sure for term. 23 and 24 of COM3 of the softstarter, so you should try both variants:
For possible connections of COM1 port of PM573, you could look in Codesys help:
Serial interface COM1 of the Terminal Bases (PM57x, PM58x, PM59x), fig. 62 and 63
Source: Codesys help COM1