Why does this timer run?

[waterboy 7]

Please look at the attached Logic and someone tell me why this Timer keeps running. The inputs are true, one by a Force and another by the LEQ statement on the second rung. So I figure it it must be a logic race so I moved it to the botton of the ladder and it made no difference. Monitoring O:0/1 and I:0/15 using a 50ms trend sample rate shows no transitions so I see no evidence of a race. Edited 29 Oct 2010 by waterboy

[Mickey 71]

With O:0/1 true and forcing I:0/15 off the XIO ( Examine if Open) instruction the rung will be true causing the timer to run. Force I:0/15 on, then rung will be false and the timer will not run. See link below for a XIC/XIO examination http://www.patchn.com/index.php?option=com_content&task=view&id=58&Itemid=74 Edited 28 Oct 2010 by Mickey

[waterboy 7]

If the input stays true, it should only run once and then set the .DN .... right? It shouldn't start over again until the input transitions again.

[Mickey 71]

Right

[waterboy 7]

It wasn't doing that, it would run constantly without the input changing state in a detectable way. The Force must interfere with the the logical state of the physical inputs.

[Bill Linne 0]

Because every time T4:13 goes DN, B3:1/10 is SET (true) for one scan. In the second rung, the fact that B3:1/10 is SET causes P1_START to be RESET (false) for one scan, which starts the entire sequence over again.

[BobLfoot 301]

Bill gets the brass ring for this one.

[waterboy 7]

Doh! I see it now. Thanks Bill.