Micrologix 1200 not talking

Our company uses micrologix 1000s for small automation projects. I recently programmed a 1200 for a small job using our laptop with a 1747-UIC adapter. The project sat for a while, and when I returned to it, I couldn't get online. I can get online with anyother Allen-Bradley plc in the shop. 1000s, 502s etc. When I try to communicate with the 1200 the LED on the bottom of the UIC adapter will systematically blink for a short while then go out. The same happens with the DCcomm LED on the processor. We purchased a new cable thinking that was the problem, but no luck. Any ideas?

The DCOMM LED should never blink; it's either OFF, or steady ON to indicate that the controller is using the Default Communications settings: DF1 Full Duplex, 8/N/1, 19200 baud, CRC Error Checking.

The COMM 0 LED, on the other hand, will blink about once per second (while disconnected) to indicate the Channel 0 serial port is in DH485 mode.

If it were my system, I would disconnect everything and verify that I can get the DCOMM LED on steady, then use a general-purpose USB/RS232 converter or RS-232 port and the DF1 Full Duplex driver.

To clarify the difference between 'blinking' and 'flickering'.

When the MicroLogix 1200 Channel 0 serial port is configured for DF1 Full Duplex and there is nothing connected to the port, the COMM 0 LED will be OFF.

When the MicroLogix 1200 Channel 0 serial port is configured for DH485 protocol and there is nothing connected to the port, the COMM 0 LED will blink for about 100 milliseconds, with about 1 second between blinks. This is a steady and consistent "blink".

When the MicroLogix 1200 Channel 0 serial port is configured for DH485 and there is an active DH485 device connected to the port, the COMM 0 LED will be steadily ON, as there will constantly be traffic on the port for token-passing.

The only times you will see the COMM0 LED "flickering" is when the port is involved in ASCII or DF1 communications, either controlled by instructions in the controller or from request from a connected device. The COMM0 LED is on only when the port is transmitting data. Because DF1 is asynchronous, the port doesn't always have data to send so the rate of "flickering" depends on how much data is being requested from the controller. Light PanelView or MSG traffic will show frequent flickering, while an upload from the controller causes the COMM 0 LED to be almost constantly ON.

In this case, it sounds to me like there's something mis-configured on the MicroLogix 1200 that is preventing it from token-passing with the 1747-UIC. Maybe it's been set for 9600 baud (the UIC only supports 19200) or maybe there's a Max Node or Node Address conflict.