USER MANUAL APS 6.0

Preface
Advanced Programming Software User Manual
15–10
Single Step Test
This mode is used with SLC 5/02, SLC 5/03, and SLC 5/04 processors. T
o use the
Single Step Test mode with an SLC 5/02 processor, you must first save and compile
your program offline with the Single Step option enabled. Refer to chapter 9 for
saving files. Note that your program size and scan time increases when you use an
SLC 5/02 processor. Refer to the Instruction Set Refer ence Manual for more
information on estimating your scan time.
The Single Step T
est mode is always available when using an SLC 5/03 or SLC 5/04
processor . Use the single step test mode to test a single rung or a group of rungs.
When you enter this mode, “SRG” appears on the status line.
When in the Single Step Test mode, the power rail character B replaces an edit zone
marker when execution reaches the break point or end rung while testing a group of
rungs. The edit zone marker is redrawn once the rung is executed. For rungs with
an I and R edit zone pair, the currently active rung will have its edit zone marker
replaced with the Single Step Test rail character.
Note The
following four characteristics ar e associated with the Single Step T est mode
(SRG) when using SLC 5/03 and SLC 5/04 processors:
• Y ou must modify your pr ogram to step thr ough a fault routine. W e r ecommend
adding a test rung containing the Jump to Subr outine (JSR) instruction to the
fault routine. Once you have done this, you will be able to step thr ough the fault
routine.
• The Selectable T imed Interrupt (STI) may appear to run 18% slower than
backgr ound timers. This will cause the pr ogram timing to be skewed between
the STI and other timers in your pr ogram.
• When stepping thr ough user interrupts, the user watchdog timer is r eplaced by
an internal softwar e timer that will expire within appr oximately five seconds.
• A STI, DII, or I/O Event Interrupt cannot occur during an I/O scan or while
servicing a communication packet. Interrupt subr outine execution will only
occur between rungs while your pr ogram is being executed.