Modicon A984-145

We have an older Modicon A984-145 with P-120 power supply, a 5-slot rack and two I/O cards from a previous project that I would like to use for a new project. When I drafted the program in ProWorx NT and configured the controller settings in the program, everything looked fine. However, when I attempted to power up the PLC and download the program I discovered that the CPU will not function. I have a good power input from the P-120 and the green LED on the power board is lit. But the Ready, Run, Modbus, and Modbus Plus LED's will not light.

I tried to download to the unit from my laptop using the serial port and a Null-modem cable to the Modbus port on the PLC but it will not communicate (time-out errors).

Is the fact that the Ready is out indicative of a "Dim Awareness" condition in the PLC? And if so, how can I download the program to the CPU if the Modbus comms will not respond? Any ideas?

how is your cable wired?look up on internet how the cable needs wired, 1 wire is probablly in the wrong place.also you have to an adapter card call sa85 to talk modbus plus, i don't remember if you need it for modbus

modbus a984-145 comm

You shouldn't need a SA85 to talk to Modbus only Plus I believe.

I think it's just tx, rx and gnd. Here is one place that claims to know the correct wiring -- http://www.broadwin.com/downloads/pdf/ModbusSerial.pdf and then you have to make sure you have the right baud rate etc. I assume you setup Nxt to have the right comms setup.

I would be a little worried about the lack of a Ready light, I'm not sure what that means (my book is not near me). I believe
you should be able to talk to it without a Run light tho.

Check that

I found the users manual available here http://www.graybar.com/automation/ga_manuals/default.htm
and it seems to show handshake lines as well on page 70. It also seems to indicate that the Ready light should be on if it passed power on diags.

Steve,

Thanks for the help. What manual are you referencing when you mention page 70? I checked the cable pinout chart in the Modicon manual and then compared it to the pinout chart in the BroadWin manual and they are slightly different. I'm still not sure if the controller is bad or not. Couldn't find the definitive answer for the status using the READY light as the indicator.

984 compact manual

From the link you have to drill down to PLC Hardaware / TSX Compact and then the "890 Use 108 00 984 Compact User Guide" -- here is the more direct link I should have used --

http://www.graybar.com/automation/ga_manuals/Hardware/TsxCompact/890USE10800%20984-A120%20Compact%20PLC's%20User%20Guide.pdf