A simple rung I just don't get

chainsaw2272

Member
C
Join Date
Jan 2014
Location
joliet
Posts
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Hello all, RSLogix 5000 one rung that i just don't understand it's purpose.
A xic and a xio with the same address in series run to a timer. Then the done bit is used in another rung.
thanks in advance
 
The programmer may not be aware that an "AFI" instruction exist in RSLogix5000 (it does)

In RSLogix5 it does

In RSLogix500 it does not ( you need to roll your own)
 
Not always leftover.... a lot of companies will make one program and have it for several versions of a machine, they will not use all of the program so they can do this to stop some features of the program/mahine but there will also be more than one rung, if this is the only run then yes odds are just troubleshooting/startup
 
I had a programmer do that to comment out rung. I absolutely hates it because it makes for very difficult reading especially if you just scan through the logic. It also make's it very confusing because you don't know if XIC or XIO was the original intention of the rung.

Needless to say, he wasn't invited back.
 
harryting said:
I had a programmer do that to comment out rung.
Click to expand...

Plus it is subtly different than "commenting out" because the rung is actually scanned, which may change the state of output instructions on that rung (e.g., de-energize an OTE).

Coming from a non-PLC programming background, I learned this the hard way.
 
geniusintraining said:
Not always leftover.... a lot of companies will make one program and have it for several versions of a machine, they will not use all of the program so they can do this to stop some features of the program/mahine but there will also be more than one rung, if this is the only run then yes odds are just troubleshooting/startup
Click to expand...

It's still not a great way of doing it when you can have a variable holding all the enable bits for functions you want as options.
 
cardosocea said:
It's still not a great way of doing it when you can have a variable holding all the enable bits for functions you want as options.
Click to expand...

I did not say it was a great way (or my way)... just a way, I have seen in the past and wanted the OP to understand there are other possibilities
 
harryting said:
I had a programmer do that to comment out rung. I absolutely hates it because it makes for very difficult reading especially if you just scan through the logic. It also make's it very confusing because you don't know if XIC or XIO was the original intention of the rung.

Needless to say, he wasn't invited back.
Click to expand...

+1

I find that dropping in a rung with an [NOP] and then commenting on that is best for grouped rungs with a common purpose. I seen a few OEM's doing it in our machinery programs, and I adopted the method myself.
 
Last edited:
JasonTheSparky said:
+1

I find that dropping in a rung with an [NOP] and then commenting on that is best for grouped rungs with a common purpose. I seen a few OEM's doing it in our machinery programs, and I adopted the method myself.
Click to expand...

This is my method. I simply learned it from seeing other peoples work and adopted the practice as well.
 
First rung of all my programs is a "always off" bit
NO and NC in series with a coil of course.
all 3 the same address.
I use the same bit designation for all my programs also.
 
Assuming an execution rate of 4ns per XIC, and a scan time of 1ms, you have a 0.0004% chance of the rung glitching every time the input turns off using the asynchronicity of the RSLogix 5000 PLC programming environment.
Same is true for bits that can change from Comms or a higher priority task.

This is non trivial for frequently changing inputs.
 
jimtech67 said:
First rung of all my programs is a "always off" bit
NO and NC in series with a coil of course.
all 3 the same address.
I use the same bit designation for all my programs also.
Click to expand...

I and a lot of people also do the same but the OP (chainsaw2272) had a timer at the end, I would never use a timer in the always off or on... maybe its a 'never timing' bit :)
 

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