Modicon 584 output state

Tech7

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Nov 2005
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Southeast Michigan
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Can someone tell me what state the outputs are in when a stop command is issued to a Modicon 584. Do they remain in their last state or do they turn off. I have some "Modicon Experts" telling me they stay on if they were on and off if they were off. I say, they must all turn off. Which is it? I would appreciate any feedback you might offer.

Tech7
 
Last edited:
584 outputs

This is old...My old manual GM-584-REF.REV-A and another printed later, page 14-13, "a latched coil retains its previous state for one scan if power is removed and later restored." This may not be as horrific as it seems. In some control functions in the old days we wanted to restore electrical function to some devices after a power failure.
 
Bruce99 said:
This is old...My old manual GM-584-REF.REV-A and another printed later, page 14-13, "a latched coil retains its previous state for one scan if power is removed and later restored." This may not be as horrific as it seems. In some control functions in the old days we wanted to restore electrical function to some devices after a power failure.

Ahh..but he was asking if you stopped the processor....dont have a clue about 584..but i know in 984 if the processor is stopped all the outputs are off..

d
 
darrenj said:
Ahh..but he was asking if you stopped the processor....dont have a clue about 584..but i know in 984 if the processor is stopped all the outputs are off..
d
Yes, when the Processor is stopped the outputs remain as the last program scan. I looked this up and dont know the reason why, but if outputs are unlatched, they are turned to off, but if latched, they retain the last scan state. This means that if the latch was on at the last scan the output is on, but if it was off the output is off. The 984 was a world ahead of the poor old 584. The manual states this was done for safety reasons.. My old program manual for the 584 repeats the warning "latching outputs must be carefully thought out before implemented". "Unpredictable machine action may result from latching outputs." :)
 
Grin....:)

The manual I refer to was printed in 1984. The revision I have is dated October 1985. It is Rev 1a. The 584 was a metal box 19" X 22". It was 76 lbs. Most had 8K memory but some had memory expansion to 32K. There were slots for 3 or 4 cards. They had 2 CPU cards and one or two memory cards. The CLX PLC I worked on today was less than one pound and could fit in one hand. It has more than 10 times the memory and a little faster processing...:) no way to compare the two.
 
lol...thats for sure...But modicon did pave the way...
never even thought to check..but does a 984 latched coil stay powered up on processor stop??
 
good question

darrenj said:
lol...thats for sure...But modicon did pave the way...
never even thought to check..but does a 984 latched coil stay powered up on processor stop??

The main frame 984A and 984B could be configured to all outputs off or on. The latch has no effect based on the configuration. The 984 A120 and other small frame PLCs seem to revert to the old "what you had last scan is what you got now". That being said, you could program a fault cleared program to set the outputs after a power failure or a prosessor restart to what ever you want. We used the prosessor status word to execute the clear memory program. In a 584 you would monitor 300105 and use the machine stop bits to reset the outputs.
 
reset outputs

I am still not sure that a 984 can reset the output table in one scan. The manuals seem to say this can be done, but if a processor is turned off and back on, do we need logic to reset the outputs or do they reset to off latch or not?
 
Thanks everyone for your reply. I originally posted this question specifically on the Modicon 584 which is a dinasour we use in our nuclear power plant. Later I posted again as a general PLC question. The engineer for this system as well as the trainer, stated that the outputs will remain in their last state when the processor is taken to stop mode. As I have found out through this forum, this would be true for a latched output. None of the outputs we were using were of this variety. Therefore our outputs all went to off. I had never dealt with this type of configuration and it seemed very dangerous to me as was stated in the 584 manual. Fortunately, we had prepared for both scenarios by recording the position of all affected valves etc.. I did learn something about the old Modicon from all of this and that is a good thing. Thanks again, especially Bruce99.


Tech7
 

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