ASCII Instructions in RSLogix500/SLC5/04

[Rube]

Before I begin what is sure to be a labor-intensive trial and error session on a running production line, I thought I might seek the advice/experience of my distinguished colleagues on the forum.

I am using Channel 0 (User mode) in a 5/04 which is RS232'd to a Microscan 860 barcode reader. I currently use the ARL instruction to capture the characters from the scanner. We are only asking to see one character at a time and the scanner is set up to send it's data with no terminating characters. I currently cycle the ARL from 0 to .50 seconds on a cycling timer set at .75 seconds. The rest of the timer is used for ASCII data manipulation; string matches, etc. The program is currently running fine....but...

I am curious how fast I can trigger the ARL instruction RELIABLY. I'm investigating a faster line speed, which means every thing must be faster. I know I'll reach a limiting factor and I'm hoping it won't be the ARL or the FIFO stacking done later in the same program.

Hopefully, each of you will enjoy this holiday season at home. Thanks in advance for any advice

 

[Doug_P]

I haven't actually used this instruction, this is just my take on it from reading the RSLogix500 help:

Once the scanner sends its data it's all sitting in the PLC's buffer just waiting to be picked up. Since the ARL uses a Register to control its operation, you can conceivably trigger it as fast as every scan.

                      R6:x/EN

------------------------(U)---



TRIGGER (ACB > 0?)                   

-----| |-------------+- ARL ----+

                     | R6:x     |

                     |          |

                     ~          ~

If you'd decide to do this, I'd incorporate the ACB (ASCII Characters in Buffer) instruction to make sure there's really something there to be read.