Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS User Manual
Page 168
Chapter 8
8Ć7
1.
Find the block transfer times of each block transfer module in the
system.
2.
Determine the sequence of block transfers for the system.
3.
Sum block transfer times according to the system sequence.
Block Transfer Time
System scan time for a PLC-2/30 remote system is the sum of processor
program scan time, processor I/O scan time, and remote I/O scan time.
For worst case calculation, assume that the Remote I/O Scanner (cat. no.
1771-SD2) can process only one block transfer operation per remote I/O
scan.
To calculate worst case block transfer time for a module, perform the
following steps:
1.
Write down known facts:
program length
number of chassis
number of block transfer modules
block lengths (W)
2.
Calculate system values determined by system configuration:
program scan time in ms
PS = (5ms/K word) x (program length)
processor I/O scan time in ms
PIO = (0.5ms/chassis) x (number of chassis)
remote I/O scan time in ms
RIO = (7ms/chassis) x (number of chassis)
3.
Calculate individual block transfer times:
write transfer time in ms
TW = PS + PIO + 2 RIO + 0.5W + 13
read transfer time in ms
TR = PS + PIO + 2 RIO + 0.5W + 4
These equations are valid for a data transfer rate of 57.6k bits/s, or 115.2k
bits/s.