AB SLC "Always on" status bit

Rick.

This is from the help-file:
This input instruction disables its rung when inserted in the condition side of the rung.

This is what I said:
This will disable scanning of the rung after the AFI instruction. (example with AFI in the beginning of the rung).

What is the difference ? :confused:
Obviously I was wrong - is it necessarry to discuss WHERE I was wrong ?
(its kinda embarrashing, you know).
 
For SLC programs I always have an always-on TRUE, an always-off AFI and reference an output NOP. That way I can enter the symbols the SLC doesn't have.



---------------------(TRUE)


-|/|--||-------------(AFI)


---------------------(NOP)


As far as 2 bits TRUE and AFI, for me it's less confusing, and at my age that's beginning to help.
 
here is my reason.

we bought a 4 station machine and the vendor had to do a lot of debug work.
they picked random bits and turned them on of off to debug. lots of bits.
they forgot several and someone turned the bit off and one station quit. i got the call at 11 pm and didn't figure it out until 3 am. we got lucky and he did the same thing on another station. i corrected the logic and got home at 4 am.
from that point on, i mandated that the first rung of logic would be an always off bit, and the second would be an always on for debug purposes.
that was *0 years ago, and i still hold to that rule every where i go.

i have not had that issue since the rule was implemented.
james
 

Similar Topics

I'm trying to read/write to an SLC5 with a ControlLogix L71 V35 plc that fails. The exact same code works on an L82S with V32. Is there a known...
Replies
9
Views
86
I'm ashamed to admit this but I've never had to replace a battery in a SLC. Some how been able to skip that task in all my years. So yesterday...
Replies
8
Views
209
I have a program that I've used 100 times. SQO settings: File N7:0, Mask 0FFFFh, Dest B3:1, Control R6:0, Length 8, Pos 2. Length & Position...
Replies
48
Views
792
Hello PLC friends. I've been going through a saga of diagnosing and fixing an old PLC setup that I inherited. I am learning as I go. Initial...
Replies
14
Views
298
I had a 5/01 CPU give a CPU Fault. It lost the program and I was not able to establish communication with it. I replaced it with a 5/03 we had in...
Replies
3
Views
111
Back
Top Bottom