RE: Moxa terminal server question PROBLEM SOLVED

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

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