Appendix A
AĆ9
I/O chassis entries in the rack list for the channel
I/O channels on the scanner that contain bloc-transfer modules
block-transfer modules on the channel (if the I/O chassis containing a
block-transfer module appears more than once in the I/O chassis rack
list, count the module once each time the chassis appears in the rack
list).)
The typical time required for the encoder module to complete a
block-transfer-read/-write (bidirectional) depends on the program scan
and the scanner scan as follows:
Time [read/write] = program scan + 2(scanner scan)
Program Scan: The program scan is approximately 2.5 ms per 1K words
or user program when using examine on/off and block instructions.
Scanner Scan: The time required for the scanner to complete a re- or
write-block transfer depends on the number of other block-transfer
modules on the same scanner channel that are enabled simultaneously.
Block-transfer times typically are similar regardless of the type of
block-transfer module, the number of words transferred, or whether a read
or write operation is requested.
A block-transfer I/O channel is a channel that contains one or more
block-transfer modules located in any chassis connected to the channel.
An I/O chassis can appear more than once in a rack list of I/O chassis.
Count the chassis and the block-transfer module(s) that it contains as
often as it is listed.
The procedure for calculating block-transfer timing for a PLC-3 processor
is given here followed by an example calculation:
1.
Determine the number of active I/O channels on the scanner and the
number of I/O channels with block-transfer modules. Show the
number of:
block-transfer modules in each I/O chassis
block-transfer I/O channels
I/O chassis entries in the rack list for each block-transfer I/O
channel
active I/O channels per scanner
