Why I couldn't not force input in PLC 5/80?

[drspanda]

Hello Everyone,

I am not having very good experience with AB PLC...I have good working knowledge with siemens...We have two plcs 5/60 and 5/80..both can be accessed by a PC.

I am not able to force an input to the 5/80 PLC but I can able to force any input to the 5/60 PLC..Why??

I have physically checked at the both processors and found identical settings (switches)..

Please help me.

 

[rdrast]

Are forces enabled in the processor? (Configurable through Logix)

 

[drspanda]

yes enabled....I could see it enabled while going on-line.

 

[Ron Beaufort]

Greetings drspanda ...



first let’s make sure that we are all talking about the same thing ...



it’s a VERY common mistake to refer to all



XIC ---] [--- or

XIO ---]/[---



instructions as “inputs” ... could that be causing your problem? ...



secret handshake: in an Allen-Bradley system, you can ONLY force ADDRESSES that begin with either the letter “I:” for “input” or with the letter “O:” for “output” ... specifically, you can NOT force an XIC or an XIO which begins with any other letter ... more specifically, forcing ANY instruction (XIC, XIO, OTE, etc.) which begins with the letter “B” will NOT work ...



now going further ... there was a certain amount of confusion with some of the earlier software packages which were previously used to program the PLC-5 family ... one specific example would be the DOS-based "A.I" software ... if you have an older version of the software, you might want to experiment with the setting of bit S:26/6 ... it’s been a long time since I’ve worked with that particular setting, but if I remember correctly, it could be used to disable “forcing” while the processor was in the Run mode ... I’m pretty sure that this was a function of the older software - and NOT a function of the PLC itself ... in other words, the newer software simply ignores the status of that bit - and always allows forcing regardless of its setting ... but ... if all else fails, you might want to take a look at S:26/6 just to be sure ...



keep in mind that what I’m writing about S:26/6 is from my memory - and I can’t guarantee that it’s 100% accurate ...

 

[drspanda]

No I am forcing the address begining with I....

 

[Ron Beaufort]

well, if nothing else works, consider posting your .RSP file and tell us which specific Input address you were trying to force ...

also please tell us what type of software (RSLogix5, A.I., 6200, etc.) and what version (3.22, etc.) of that software you're using ...



as it stands, I've personally never seen any "I:" address that I could not force ... but ... going deeper ... is it possible that someone has "hijacked" the status of the input by using ladder logic? ... this sometimes happens by mistake ... but occasionally it is done as a “temporary” repair (not recommended) ...



if that’s your problem, then this post should help you understand the concepts involved ...

 

[OkiePC]

I don't have RSLogix5 anymore and I don't know the addresses to search, but just maybe the original programmer played a little trick by continuously unlatching the forces enabled bit in ladder logic. Just a thought...

 

[Mickey]

I don't have RSLogix5 anymore and I don't know the addresses to search, but just maybe the original programmer played a little trick by continuously unlatching the forces enabled bit in ladder logic. Just a thought...

 

[tnk786]

Solution

for your solution, if u want to force an I, first change the radix to binary and then individually force the bits of I (16 bits) according to the decimal number you want to force e.g to force a value of 4 just make the 3rd bit as 1 and leave others as 0. It will definitely work

Tahir

 

[Operaghost]

......I am not able to force an input to the 5/80

What precisely do this mean? Do you get an error? What isn't working?

Have you tried opening the Input Force file and manually typing a 1 or a 0? What happens when you try this? Don't forget, after adding a force, you must ENABLE forces. It's a two step process.

OG

 

[Operaghost]

Mickey, what you have shown in your screen shot is Force Status. What Ron is referring to is on the Control tab.

Run Mode Memory Protection S:26/6
(Valid when using enhanced PLC-5 processors only) Set this bit if you must restrict forcing or data table changes. When (0) the data table and forces can be edited in Run mode; when (1) the data table and forces cannot be edited when the processor key switch is in Run mode.

OG

 

[Operaghost]

Another possibility is the use of passwords/privileges. The user Class could have that feature locked out.OG

 

[Mickey]

Mickey, what you have shown in your screen shot is Force Status. What Ron is referring to is on the Control tab.



OG

What I'm referring to is OkiePC's post. What if the program had this
EDIT: I just tried it and it still let me force an output.