Can't Connect to RSLinx with SLC 5/03 and SLC 5/04 Processors

Hello All,

I’m trying to connect some SLC 5/03 and SLC 5/04 processors to RXLinx but am unable to see the connection to the processor in the RSWho screen. I tried to restore the processors to initial factory conditions then found that when hooking up power the DH485 light was slowly blinking green and the fault light was blinking red, thus I believe if the restore worked the processors should be defaulted to channel 0 and the DH485 protocol should be used, however the restore should have also removed any faults if it did work.

When using two different RS-232-USB converters I proceeded to RSLinx and tried to configure drivers using driver types: DH485 UIC devices, 1784-PKTX(D)/PCMK for DH+/DH-485 devices, 1784-U2DHP for DH+ devices, and finally RS-232 DF1 devices both in auto configure and trying the following configuration which I found on a tutorial: Baud Rate: 19200, Station Number: 00, Parity: None, Error Checking: CRC, Stop Bits: 1, Protocol: Full Duplex.

I’m not sure why I can’t connect to RSLinx, any help here is appreciated.

Welcome to the PLCTalk forum community !

In general, disconnecting the battery and following the instructions to drain the capacitor by shorting the Vdd/GND pads will clear the user program, and you will see a flashed red FLT indicator.

EDIT: THE BELOW ANSWER MIS-READ THE NAMED SLOW-BLINKING GREEN LED AS RS-232, NOT DH485 AND IS INCORRECT

Please confirm that the RS-232 activity indicator LED is flashing green at about 1 Hz when *nothing* is connected to it.

The Channel 0 RS-232 port on an SLC-5/03, /04, or /05 controller flashes at 1Hz when disconnected only when the port has been configured for DH485 protocol. If it is set for DF1 or ASCII protocol, it flashes only while transmitting data, which it can't do if the user program has been erased and it's disconnected.

The default settings for the Channel 0 RS-232 port on those controllers is DF1 Full Duplex, 19200 baud, 8/N/1 framing, CRC error checking.

So I think you've still got a program in these controllers that is setting the Channel 0 serial port for DH-485 protocol over RS-232.


To connect to a port in that state, you need either a 1747-UIC, or an old computer with a built-in serial port and an OS no newer than Windows XP SP2 or SP3+patches. General purpose serial/USB converters are only going to work with DF1.

Let me try again. Welcome to the forum ! I'm still cooking pasta sauce and haven't even gotten into the wine yet.

That slow-blinking DH485 network port LED on the SLC-5/03 is normal when it's disconnected.

So let's examine those USB/RS232 converters. Can you post what make/model you're using ?

You do need a "null modem" cable between the serial port on your PC and the Channel 0 RS-232 serial port on the SLC-5/0x. The A-B part number is 1747-CP3, but any null modem cable that swaps pins 2 and 3 (and runs pin 5 straight through) will work.

Many USB/RS232 converters can't keep up with the rapid changes to the framing setting that are done by the Autoconfigure feature, so I like to stick with 19200 8/N/1 CRC.

Double, triple, quadruple-check the COM port number that your USB-serial converter is using.

Thank you for the warm welcome Ken Roach! RE. the flashing red FLT and the slow blinking DH485 lights that’s a good sign, the Allen-Bradley PDF I was reading through didn’t mention that was normal after a factory restart.

In terms of the USB/RS232 converter, I’m using a StarTech ICUSB232 which is a USB to male end serial port which I then connect to the processor with a female to female DB9 cable. After lurking through forums today I’ve found that this isn’t a commonly used converter for what I’m trying to accomplish so I may have go with a more trusted solution.

I’ve tripe checked the COM port and noticed when I use the wrong one an error message about not being able to connect with the port pops ups and I check the device manager each time to ensure it’s the same.

I’m going to do a continuity check on my null modem cable to ensure that what you’ve stated "any null modem cable that swaps pins 2 and 3 (and runs pin 5 straight through)" is what I have.

Thanks Ken for your quick reply and I’ll post what I find with the cable!

I think you are this close:

Hello Ken Roach and OkiePC,

You both were absolutely correct; my null modem cable was the issue as it didn’t match the pinout of the AB cable: 1747-CP3. I did some digging on this forum and found that only the three connections you mentioned were needed, common pin number 5 and tx/rx pin number 2 and 3 which are of course swapped between the two DB9 serial connectors. After connecting three jumpers to test the connection I was able to auto configure with no issues on RSLinx!

Thanks again for your help guys and have a great day!