Comparing numerous words

Hi,

I need to check that 12 marker words are all equal to zero.

The words are made up of individual fault bits that are set if there is an error (e.g. "Pump Overload","Coolant Level Low" etc etc) 

I would like to test that there are no alarms current.

I am working in LAD but immediately came across the problem of non-integer words whilst writing the chained [Compare if = to zero] instructions in ladder.

Would rather not move contents of words to new INT marker words, but quite happy to have one network in STL for this.

What do you think would be the best way to chain the 'load and compare to zero' statements to set one marker bit indicating there are no faults present?

Thanks in anticipation of a reply. 

Hi rlmts,

You need not to define alarm register as word. Even though u define it as integer, you can use its bits for various alarm status.[MSB is not influenced by CPU]. Just define it as integer and use LAD to compare.

rlmts

I need to check that 12 marker words are all equal to zero.

Hi.

The trick is to use the INT compare instruction within STL.

For your special {zero} case..

L   alarms1 // 1st alarm word
OW  alarms2 // WORD OR instruction
OW  alarms3 //..you repeat for all 12 WORDS
L   0       // zero
==I         // INT compare!
=   bitsZero

Regards.

William_B

rlmts

I need to check that 12 marker words are all equal to zero.

Hi.

The trick is to use the INT compare instruction within STL.

For your special {zero} case..

L   alarms1 // 1st alarm word
OW  alarms2 // WORD OR instruction
OW  alarms3 //..you repeat for all 12 WORDS
L   0       // zero
==I         // INT compare!
=   bitsZero

Regards.

 Another trick

L   alarms1 // 1st alarm word
OW  alarms2 // WORD OR instruction
OW  alarms3 //..you repeat for all 12 WORDS
A   ==0     //is ACCU1=0 ?
=   bitsZero

Correction:

Although it looks good it doesn't work like that.

L   alarms1 // 1st alarm word
L   alarms2

OW          // WORD OR instruction
L  alarms3 //..you repeat for all 12 WORDS

OW
A   ==0     //is ACCU1=0 ?
=   bitsZero

Hello Jacek,

Can you explain in more detail please.

Thank you  

OW instruction can act on ACCU1 and ACCU2 (i.e. variables loaded to both ACCUs) directly like below: 

L variable1

L variable2

OW

Or it can combine a variable in ACCU1 with a constant: 

L variable1

OW constant_16bit //e.g. w#16#1111

But above construct can't be used with two variables. I.e. code below is incorrect: 

L variable1

OW variable2 //OW instruction can't be followed by variable

The OW instruction (and few others) changes additionaly some special flags (bits) in so-called status word (STW). The flags describe the contents of the ACCU1 (i.e. the result of the last operation). Thanks to this, it can be checked e.g. if ACCU1 is 0 directly, i.e. without explicit comparison, like in the code below: 

A   ==0     //is ACCU1=0 ?
=   bitsZero

Hi Jacek,

Thanks for the explanation. 

I thought I understood your reply until I tried to adapt it to test a number of words. 

Am I correct in saying that the instruction to load the contents of a word into the accumulator is not RLO dependent? In which case, how can I chain test a number of words?

 Thanks Jacek for correcting my error and expanding on this thread.

---

rlmts

Hi Jacek,

Thanks for the explanation. 

I thought I understood your reply until I tried to adapt it to test a number of words. 

Am I correct in saying that the instruction to load the contents of a word into the accumulator is not RLO dependent? In which case, how can I chain test a number of words?

@ rlmts.. You are right about the RLO.
How did you code the 12 WORDs?
Try this:

SET
L   alarms1
L   alarms2
OW
L  alarms3
OW
L  alarms4
OW
L  alarms5
OW
L  alarms6
OW
L  alarms7
OW
L  alarms8
OW
L  alarms9
OW
L  alarms10
OW
L  alarms11
OW
L  alarms12
OW
A   ==0     //is ACCU1=0 ?
= bitZero

Note there is no spacing in "==0".

Regards.

OK, thanks everyone