"Test ASCII Buffer for Line" Instruction for AB SLC 500

Andrew Evenson · Sep 13, 2006

Hi all,

I'm trying to use the "Test ASCII Buffer for Line" Instruction in a AB SLC500, and are having some trouble. What I am having trouble with is with the ".FD" bit. I see all the bits in the element R6:1 being reset it I initiate a Reset on R6:1, except the .FD bit doesn't reset. What has to happen to reset this bit?? Do I have to externally unlatch it??

Hope I have expalined my problem properly...

Andrew Evenson

Ken Roach · Sep 13, 2006

What precisely do you mean by "initiate a Reset on R6:1" ? The RES instruction is intended for Timers and Counters only, and I haven't seen it used on a Control Register (R-type data file element).

You shouldn't ever externally manipulate any of the bits in the control file except the .UL Unload bit if you need to manually cancel the instruction.

With both ASCII and MSG instructions, I often condition the .DN or .FD bits with a oneshot to trigger another instruction in my program.

Doug-P · Sep 13, 2006

Ken Roach said:
What precisely do you mean by "initiate a Reset on R6:1" ? The RES instruction is intended for Timers and Counters only, and I haven't seen it used on a Control Register (R-type data file element).

Ken, I have used a RES on register elements, and with no ill effects. Specifically, on an FSC instruction inside a subroutine.

This is done because at each invocation of the subroutine the search must start at the beginning of the file. Without the reset, if the search argument had been found during the previous scan the instruction would start searching from a point other than the start of the file. I don't have the logic in front of me but I think I also had to explicitly unlatch the FD bit to get the search to operate correctly. I'm pretty sure also that unlatching the FD bit on a search instruction is documented in A-B literature.

An alternative to this is to place an identical search instruction, in an unconditionally false rung, just before the 'real' search begins.

R_C · Sep 13, 2006

The .FD bit should be off while the instruction is enabled. It will be on when the termination character is found. Set the termination character under Channel configuration > Chan. 0 User

Andrew Evenson · Sep 19, 2006

Gentlemen,

I am sorry it has taken so long for me to respond to your replies, been very busy at here over the last few days of last week and yesterday.

Ken:

The reason I asked about using a reset instruction is that we currently have a running program that uses the reset instruction to reset control registers of ASCII read and write instruction. Because of this I thought it was normal. Guess I was wrong.

R_C:

Your response is what i was looking for; and that is how the instruction is working. I see the .FD bit set when it encounters the end of string terminator, but what I'm not seeing is it reseting. How is it suppose to reset?? When the rung with the "Test ASCII Buffer for Line" Instruction goes from true to fasle to false to true again???

Thanks again for all your replies!!

Andrew Evenson

R_C · Sep 26, 2006

Andrew Evenson said:
Gentlemen,

I am sorry it has taken so long for me to respond to your replies, been very busy at here over the last few days of last week and yesterday.

Ken:

The reason I asked about using a reset instruction is that we currently have a running program that uses the reset instruction to reset control registers of ASCII read and write instruction. Because of this I thought it was normal. Guess I was wrong.

R_C:

Your response is what i was looking for; and that is how the instruction is working. I see the .FD bit set when it encounters the end of string terminator, but what I'm not seeing is it reseting. How is it suppose to reset?? When the rung with the "Test ASCII Buffer for Line" Instruction goes from true to fasle to false to true again???

Thanks again for all your replies!!

Andrew Evenson

Use the OTU instruction on the .FD bit when you are done using the .FD bit.

"Test ASCII Buffer for Line" Instruction for AB SLC 500

Andrew Evenson

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R_C

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Andrew Evenson

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R_C

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