Report pulse and sub routine in Vision & Samba PLC + HMI Controllers & VisiLogic Software Posted November 15, 2012 It is generally understood no matter whose platform you use that the transitions are based off WHEN in the program that bit of memory gets written resulting in a change of state. It is not (should not be) be directly related to the "housekeeping" portion of the scan. However, if you are reading physical Inputs, then those are updated only during the "housekeeping" portion of the scan. Unless of course you use an immediate IO read to sample the hardware IO before the "housekeeping". Since MB bits are internal, there is no housekeeping necessary for them, therefore the end of the scan is irrelevant. In addition, if you have conditionally executed subroutines in a PLC (which should normally be avoided for a host of reasons) your code may completely miss transitions that came and went because the transitional instruction you are using will base that off of the evaluation of that instruction the previous time it was exectued. On the flip side, you could have the same bit (MB) of memory trigger positive and negative transitions multiple times in one single scan.