We recently ran into an unusual problem converting
a program from a SLC5/04 to a PLC-5/11 and was wondering if anyone else has encountered this issue. Perhaps someone knows the reason for the problem and has found a solution.

Hardware:
PLC-5/11, PanelView1000-keypad only, connected via DH+

Software:
RSLOGIX-5, version 3.22.00, PanelView firmware v.3.4
An original program used on a SLC-5/04 was converted to PLC-5/11 by cutting and pasting the ladders and manually converting all necessary commands to their PLC-5 equivalents.

Symptoms:
The FLL (filefill) command is used to turn HMI bits off at end of scan. This operates correctly so long as the ladders do not exceed 7 and total memory use does not exceed 5000kb. If either of these is exceeded, the pushbutton operation of the PanelView begins to degrade and eventually ceases. All reading operations and numeric entry are unaffected and work properly. Only the writing of bits to the PLC are affected.

The JSR command apparently contributes to this problem. If they are removed, the pushbuttons operate normally again.

Our Solution:
After experimenting with the system and observing the scan times, it was clear something was causing the processor to slow down drastically. (This is how we saw the JSR command was part of the problem.)

Using the MCP screen, the subroutines are called via configuration instead of by coding. This replaces the need for using JSR commands. The application now works properly.

Question:
Since we are unfamiliar with all the nuances of the MCP, can anyone confirm that it forces the servicing of I/O? We rarely make conversions between SLC-5/04 and PLC-5/family softwares. Are
there issues at work here that are not well documented?

Any other insights are greatly appreciated. I can be contacted personally at the address below if you require more information.

Best regards,
Ruel V. Alejaga
Systems Engineer
E-mail:[email protected]

Control Masters, Inc. Voice: 630-968-2390 x309
5235 Katrine Avenue FAX: 630-968-3260
Downers Grove, IL 60515

 

> Symptoms:
> The FLL (filefill) command is used to turn HMI bits off at end of
> scan. This operates correctly so long as the ladders do not exceed 7

IIRC, if you are using DH+, the communication scan is asynchronous to the program scan on a PLC5. Thus is you are turning all the bits off at the end of the scan, its possible your PLC is not actually seeing them sometimes.

Best thing to do is to check to see if the word the PB bits are in is not zero for some period of time, and then turn them off.

Curious, why do you even bother? The Panelview can turn them off just as easily.

 

I am a little confused but it appears that you may have been getting caught in endless loops. I am not sure how you were configured but I do the same thing with JSR to subroutines all the time.

Did you have the JSR and the MCP configured at the same time.....?

After the MCP (Master Control Program) scans, yes the I/O is updated. Whereby in a JSR, all of the code from start to finish will run and then the I/O update takes place. So another words you can have 2 MCP's running asyncronously to each other. I rarely have a need to do this. How do you do the FFL's, were you overwriting data with other data because of the I/O update at the end of the scan with the JSR's.

What kind of scan times are you seeing from the MCP etc.

Still think you had some kind of looping tying up your processor. I have run these for ages and had little to no problems I did not create myself.

E-mail if you have questions would be happy to discuss issue with you via e-mail. Hard to diagnose without the entire story.....

Dave Ferguson
[email protected]