Folks,
I have solved the problem, and I can now program the SLC500 through the Moxa.
I enabled data logging on the Moxa and I saw that the received data from the PLC was identical to transmitted data to it. I then found that this was true even when the
PLC was off! It was clearly a cable problem, as Mark K. suggested.
I misread the pinout of the RJ45 connector on the Moxa. Interestingly, although EIA-561 specifies the pinout for RS-232 on RJ45, I have yet to find a vendor who actually
follows the EIA-561 standard. Moxa and ProSoft use a completely different pinout.
Function
|
EIA-561
|
Moxa NPort
|
ProSoft MVI46-MNET
|
TxD
|
Pin 6
|
Pin 4
|
Pin 3
|
RxD
|
Pin 5
|
Pin 5
|
Pin 2
|
GND
|
Pin 4
|
Pin 3
|
Pin 5
|
Once I wired the connector properly, the RSLinx Autoconfigure worked and I can program via the Moxa.
Thanks,
Mark
From: Mark Rivers
Sent: Thursday, February 16, 2023 11:45 AM
To: tech-talk at aps.anl.gov
Subject: Moxa terminal server question
Folks,
I have an Allen-Bradley SLC5/03 PLC. I use an RS-232 connection from a Windows PC to the PLC for programming it. This works fine when I connect to a real serial port on the PC. However, that is inconvenient because that is over 50 meters
from the PC, and I have 2 PLCs and only 1 serial port, so I need an A/B switch. I would like to use a multi-port Moxa terminal server instead. I have installed the Moxa software on the PC that makes COM2 appear as a Windows COM port, using one of the serial
ports on the terminal server.
I then try to configure the Allen-Bradley RSLinux software to use COM2 with their DF1 protocol using the “Auto-Configure” option. This “almost” works. If I disconnect the serial cable from the Moxa to the PLC and run Auto-Configure it
fails to find the matching baud rate and parity. This is expected of course, since it is not communicating at all. If I connect the cable it does correctly find the baud rate and parity, so it is communicating OK. However it then reports “Failed to dine
error checking mode!”. There are 2 choices for error checking, BCC, and CRC. Both fail.
I don’t understand this, since I think the BCC and CRC are both done in software on the PC end. If the Moxa is providing sufficient emulation of a COM port to allow the baud rate and parity to be configured OK, why it is failing to configure
the error checking?
Any ideas are welcome!
Thanks,
Mark