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Block transfer Timing for PLC 2
Family Processors
Block transfer Timing
The time required for a block-transfer-read or -write operation for PLC-2
family processors depends on:
the system scan time(s)
the number of words to be transferred
the I/O configuration
the number of enabled block-transfer instructions in the ladder diagram
program during any program scan
A block-transfer module performs only one block-transfer operation per
I/O scan regardless of whether both read and write operations are
requested. When done, the module toggles from one operation to the
other in each program scan.
For a worst case calculation of the time between block transfers, assume
that the number of enabled block-transfer instructions during any program
scan is equal to the number of block-transfer modules in the system. Also
assume that the encoder module is transferring 20 words in a write
operation and two words in the alternate read operation.
The method of calculating the worst case time between block transfers is
covered for the following case: PLC-2/30 remote and local systems, a
PLC-3 system, and a Mini-PLC-2/l5 controller.
PLC 2/30 (PLC 2/20) Remote System
The system scan time for a remote PLC-2/30 or PLC-2/20 system is the
sum of the processor scan time, the processor I/O scan time (between
processor and remote distribution panel), and the remote distribution
panel I/O scan time. The remote distribution panel can process only one
block-transfer operation per remote distribution panel scan.
You can calculate the worst case time between transfers under normal
operating conditions in three steps.
1.
Calculate the system values that are determined by the system
configuration.
A
Appendix
A 1
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