ControlLogix reading SLC5/04.

Patrick · Jun 26, 2010

Using a message box in ControlLogix to read from a SLC5/04 on DH+. The correct tag is being read, but the wrong info is coming through. I should be seeing the number 23 but I see 2228247. If I change the number by 1 in the SLC then the number in the ControlLogix will change by one. If I change the Source address, It might read the right number or it might read some other number but it is looking at the correct address.
Pat

Ron Beaufort · Jun 26, 2010

try this ...

make sure that your tag is set for INT - not for DINT or anything else ...

the older SLC-5/04 "thinks" in a 16-bit integer format ... the newer ControlLogix usually has a default setting of DINT - which is a 32-bit format ...

if that's not your problem, tell us more about the location (tag) in the ControlLogix and we'll help you nail this down ... it would also be nice to know the address of the location in the SLC ... the more we know, the more we can help ...

Patrick · Jun 26, 2010

Ron Once again you hit the nail on the head. I have three SLC500/04 that I read n7:21. The first two give me the correct reading the third is way out. They all read by the same message command. So why does a Dint. Tag work for the first two and not the Third? All three where new at about the same time.

Pat

lostcontrol · Jun 26, 2010

So the problem is still there?
Maybe try disabling whatever is writing to N7:21 & N7:22, then manually put the same values in each & see what ends up in the CLX.
If they are not the same, then there has to be something fundamentaly wrong, if they are the same, then re-enable whatever writes to them, & try & locate whatever is writing incorrect data.

Gil47 · Jun 26, 2010

Patrick said:
I should be seeing the number 23 but I see 2228247. .
Pat

The Binary of 2228247 Dint is 100010---0000000000010111 broken at 16 bits

The integer of those binary number is 34 --- 23 two numbers in concecutive words in the 5/04

Patrick · Jun 26, 2010

HI Lostcontrol. Ron’s subjection to use the INT instead of the Dint Did work. The problem is WHY? If I am using a DINT for the first two I should be able to use the DINT on the third one. But I can’t. The INT does work on all three. If I change the address in the same controller, it might read 16 bit or 32 bit. I have the number 23 at address N7:21 and the number 40 at N7:22. N7:22 will read 40 with the DINT tag but N721 would read 2228247 with the Dint tag. The both read the correct number with the INT tag.

But the way nothing is writing to ether tag. They’re just place holders.

Gil thanks. I thought that was what happen, one number converts to 16 the other to 32.

Pat

sthompson · Jun 26, 2010

Patrick said:
HI Lostcontrol. Ron’s subjection to use the INT instead of the Dint Did work. The problem is WHY? If I am using a DINT for the first two I should be able to use the DINT on the third one. But I can’t. The INT does work on all three. If I change the address in the same controller, it might read 16 bit or 32 bit. I have the number 23 at address N7:21 and the number 40 at N7:22. N7:22 will read 40 with the DINT tag but N721 would read 2228247 with the Dint tag. The both read the correct number with the INT tag.

But the way nothing is writing to ether tag. They’re just place holders.

Gil thanks. I thought that was what happen, one number converts to 16 the other to 32.

Pat

I think Ron and Gil47 has alluded to the correct answer. I will bet if you look, the two SLCs that are working have zero in N7:22, but the SLC giving you the problem has a number in it. I will have to try it on Monday, but I suspect because you are using DINTs at the ControlLogix end, the Message Instruction is reading two consecutive Integers out of the SLCs. At the Bit Level, these are two completely different numbers when evaluated as a 32 Bit DINT.

Stu.....

Patrick · Jun 26, 2010

sthompson. Thank you for opening my eyes. You’re absolutely right. When I put a zero in N7:22 of the same unit with the problem. The problem when away.

disclaimer: if this doesn't work the way I "think" it will, please remember that I'm not there with the system - but doing the best that I can anyway ...

Ron. From what I see when I read the post out here, you do a beautiful job.
Keep up the good work.

From now on I will use INT when dealing with SLC or PLC.

Thanks Pat

ControlLogix reading SLC5/04.

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