Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 178)

ASCII Module
PLC-2 Family Processors
Appendix A
AĆ10
The facts of the problem are:
Program length = 4K words
Number of chassis = 4 rack numbers
Number of block transfer words = 64 words (read), 2 words (write)
1. Calculate the system values.
Processor Scan Time PS = (5ms/1K words) x (4K words) = 20ms
Processor I/O Scan Time PIO = (0.5ms/rack number) x (4 rack
numbers) = 2ms
Remote Distribution I/O Scan Time RIO = (7ms/chassis) x (4 chassis) =
28ms
Number of Words Transferred = 64 (read) or 2 (write)
2. Calculate the block transfer times, TW for a write and TR for a read
operation.
TW = PS + IO + 2(RIO) + 0.5W + 13
TW = 20 + 2 + 2(28) + 0.5(2) + 13
TW = 92ms (write)
TR = PS + PIO + 2(RIO) + 0.5W + 4
TR = 20 + 2 + 2(28) + 0.5(64) + 4
TR = 114ms (read)
3. Calculate the worst case system time ST between 2 consecutive read
block transfers.
ST = 4TW + 4TR
= 4(92) + 4(114)
= 368 + 456
824ms
This is the worst case time between two consecutive read block transfers
in the 4-chassis remote configuration described in example problem 1
(enabled ASCII module in each chassis).