MLX 1400 Serial Issue

This one is just weird.

I have a device which has been working great. I have done comms tests repeatedly with different PCs emulating serial strings coming from a Micrologix 1400. I finally connected my device to channel 0 using a custom cable (pins 2, 4, and 7) and my device died. While troubleshooting I realized that I forgot to switch the channel configuration from DF1 to ASCII, but I don't think that would have killed it.

Upon reading the manual further I saw some info about not connecting to certain pins due to voltage issues, but I didn't see anything regarding the mistake I had made. It could be some other factor (ESD, etc), but I'm trying to rule out any mistakes I made before I go through the trouble to build a new unit and connect it again.

Thanks,
-J

I have a device

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does your device have a name? it might help others to help you if more info is provided.

Just to clarify, were you connecting to the round 8 pin connector or the 9 pin "serial" DB9 connector?

TWControls said:

Just to clarify, were you connecting to the round 8 pin connector or the 9 pin "serial" DB9 connector?

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Thank you for replying.

I was using the round 8 pin connector.

The only two thoughts I have without knowing more about the device you are connecting to is:

Verify your pinout. If you completely reverse the pinout then pins 4 and 7 will be correct, but pin 2 would be connected to pin 1 which has 24V

Check the minimum resistance of your device. Does it have any type of isolators on the communications channel?

On the Channel 0 serial port (round Mini-DIN8) of the MicroLogix 1100 and MicroLogix 1400 controllers, Pins 1 and 8 are the Data A and Data B RS-485 connection.

On the Channel 0 serial port of the MicroLogix 1000, 1200, and 1500 controllers, Pins 1 and 8 are the 24V DC auxiliary device power supply.

If your serial device could be damaged by connection to an RS-485 port, then it's possible you mis-wired the cable. If not, then it's probably a coincidence or an ESD/ground issue.

Ken Roach said:

On the Channel 0 serial port (round Mini-DIN8) of the MicroLogix 1100 and MicroLogix 1400 controllers, Pins 1 and 8 are the Data A and Data B RS-485 connection.

On the Channel 0 serial port of the MicroLogix 1000, 1200, and 1500 controllers, Pins 1 and 8 are the 24V DC auxiliary device power supply.

Click to expand...

Thanks for the correction Ken. I'm so used to that pesky 24V being there...