USER MANUAL 1771-DCM User Manual

Calculating Transfer Time
Chapter 7
73
Processor Multiplier
PLC2/05, 2/15 0.08
PLC2/30 (Local) 0.08
PLC2 Family Example Computation
Suppose that a PLC-2/30 supervisory processor has a 6K program and
seven assigned rack numbers and the PLC-2/05 local processor has a 2K
program. There are no other block transfer modules in either the
supervisory or local systems.
1. Calculate the time required to transfer eight words from supervisory
to local processor.
2. Calculate the total time required if there are two additional block
transfer modules in the local chassis, transferring 64 words each.
Assume worst case.
Solution Part 1:
PLC-2/30 Supervisory Processor Scan Time:
Scan PLC2/30
Program 5 ms/K Words
Processor I/O 0.5 ms/Rack
Remote I/O 7 ms/Chassis
Time (PLC-2/30) = Program + Processor I/O + Remote I/O
= (5 ms)(6) + (0.5 ms)(7) + (7 ms)(7)
= 30 ms + 3.5 ms + 49 ms
= 82.5 ms
1771-DCM Delay: 15 ms
Local Processor Scan Time:
Time for PLC2/05
I/O Scan 1 ms
Program Scan 15 ms/K
Block Transfer 0.08 ms/W