PACSystems™ RX3i and RSTi-EP CPU Reference Manual Appendix A
GFK-2222AK October 2019
Serial I/O, SNP & RTU Protocols 200
configuration with no I/O modules or intelligent I/O modules (GBC) has the same effect.
The logic execution time is not zero in the base sweep. The time to execute the empty
_MAIN program is included so that you only need to add the estimated execution times of
the functions actually programmed. The base sweep also assumes no missing I/O
modules. The lack of programmer attachment means that the Controller
Communications Window is never opened. The lack of intelligent option modules means
that the Backplane Communications Window is never opened.
A-3.2 What the Sweep Impact Tables Contain
In some tables, functions are shown as asynchronously impacting the sweep. This means
that there is not a set phase of the sweep in which the function takes place. For instance,
the scanning of all I/O modules takes place during either the input or output scan phase
of the CPU’s sweep. However, I/O interrupts are totally asynchronous to the sweep and
will interrupt any function currently in progress.
The communication functions (with the exception of the high priority programmer
requests) are all processed within one of the two windows in the sweep (the Controller
Communications Window and the Backplane Communications Window). Sweep impact
times for the various service requests are all minimum sweep impact times for the
defined functions, where the window times have been adjusted so that no time slicing
(limiting) of the window occurs in a given sweep. This means that, as much as possible,
each function is completed in one occurrence of the window (between consecutive logic
scans). The sweep impact of these functions can be spread out over multiple sweeps
(limited) by adjusting the window times to a value lower than the documented sweep
impact time. For the programmer, the default time is 10 ms; therefore, some of the
functions listed in that section will naturally time slice over successive sweeps.
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