CompactLogix I/O Green Light Flashing while Powerup


Thread Starter

Mayuresh Kulkarni

Why is the I/O LED on CompactLogix Controller L32-E flashing Green? This PLC setup currently has the Controller, the 24V DC power supply and 5 Digital I/O cards tied up together on a DIN Rail with proper grounding as suggested.

I tried to look up for what the flashing green LED could mean and documentation says that one or more I/O is not responding? .. I have powered up this PLC without actual I/O wires connected to the Digital I/O Cards. At powerup, now it has the I/O LED flashing green. I wonder if it has to do anything with actual I/O wires not being hooked up these I/O cards or if there's something wrong with one or more backplane connections at the I/O cards or if its an I/O card gone bad? What could be the most likely reason? How can I trouble-shoot this problem?
Please advise.

Bob Peterson

Take a look at the I/O configuration and see if any of the cards show any anomolies. Could be some minor error like a card incompletely configured, or a blown fuse.

Mike McDermott

When they say "I/O not responding" they are referring to the I/O cards you have setup in your rack, not the actual wired I/O. The PLC doesn't know if the sensor at the end of a wire is working or not, simply the card. What you have is one of several things. First, make sure the card you have setup in your I/O tree in your Logix 5000 software is the same card you actually have in the rack. 2nd, go to the properties of the card you have setup and look at the version number and compare it to the version number on the sticker located on the I/O card. The minor rev level shouldnt matter but the major rev level does. Thirdly, under the properties of the I/O card again, look at the keying. Make sure you dont have "exact match" selected. I always use any compatible or have even used no keying. Very seldom if ever have I used "exact match". The last thing I would look at if all that is ok is to make sure you have flashed the I/O card. Some cards do not require a firmware flash while others do. If it is a standard Digital input module, it probably does not but if all else fails, you could reflash it, just make sure you don't interupt the flash process or you will be hosed. Like I said, the I would look at all other things I mentioned before worrying about flash. If you look at your I/O tree in logix 5000 (while online) there will be a yellow symbol over the I/O that is not responding so that should help you narrow down which one(s) are not responding and go from there. My first guess would be that you have a rev level mismatch or the keying is set to "exact match".

I have problem with flashing I/O light too. When I turn on the PLC the I/O light flashing and status lights on all modules are green for 2-3 seconds. Then all modules' lights turn off for one second and again on. This is happened over and over again and only when I use two banks. When I disconnect second bank all is ok. I have this problem even when in second bank is only power module.

Sorry for my english but I'm from Poland. :)

Ricardo Godoy

Depending on firmware versions, you might have problems like this. It also happens with Drive Logix.

You can create a small logic using SSV to disable all I/Os in power ups. Reading SSV intruction help, you can see that write int "4" into "source", with atribute name parameter "mode" and instance name "module name" you desable one I/O card. You need to make a SSV instruction for each module. So, the logic must be:

First scan (S:FS bit) enable a timer (5000 ms), while the timer is not done, move int 4 to SSV source instruction. After is done, move int "0" to "source" and your problems are for sure past problems!!!!

Ricardo Godoy