PACSystemsâ„¢ RX3i and RSTi-EP CPU Reference Manual Appendix A
GFK-2222AK October 2019
Serial I/O, SNP & RTU Protocols 206
Sweep Impact of Genius I/O and GBCs
For the sweep impact of Genius I/O and Genius Bus Controllers (GBC), there is a sweep
impact for each GBC, a sweep impact for each scan segment, and a transfer time (per
word) sweep impact for all I/O data.
The GBC sweep impact has three parts:
1. Sweep impact to open the System Communications Window. This is added only
once when the first intelligent option module (of which the GBC is one) is placed
in the system.
2. Sweep impact to poll each GBC for background messages (datagrams). This part
is an impact for every GBC in the system.
Note: Both the first and second parts of the GBC’s sweep impact may be eliminated by closing the
Backplane Communications Window (setting its time to 0). This should only be done to
reduce scan time during critical phases of a process to ensure minimal scan time. Incoming
messages will timeout and COMM_REQs will stop working while the window is closed.
Sweep impact to scan the GBC. This results from the CPU notifying the GBC that its new
output data has been transferred, commanding the GBC to ready its input data, and
informing the GBC that the CPU has finished another sweep and is still in RUN Mode. Scan
segment for a Genius I/O block consists of consecutive memory locations starting from a
particular reference address. A new scan segment is created for each starting input or
output reference address. The time to process a single scan segment is higher for an input
scan segment than it is for an output scan segment. The scan segment processing is the
same for analog, discrete, and global data scan segments. Discrete data is transferred a
byte at a time and takes longer to complete the transfer than analog data, which is
transferred a word at a time. Global data should be counted as either discrete or analog,
based on the memory references used in the source or destination.
Sweep Impact Time of Genius I/O and GBCs
Note: Functions in bold type impact the sweep continuously. All other functions impact the sweep
only when invoked. Not all the timing information listed in the following table was available
at print time for this manual (the blank spaces).
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