Rockwell Automation 1771-DCM USER MANUAL 1771-DCM - Manual (Page 40)

Calculating Transfer Time
Chapter 7
7Ć6
Solution Part 1:
Time (1 Module) = (5 ms)(4.8) + (0.5 ms)(6) + 2(7 ms)(6) + (0.5)(64) +
10
= 24 ms + 3 ms + 84 ms + 32 ms + 10 ms
= 153 ms
Total Time (All Five Modules) = 5(153)
= 765 ms (Worst Case)
Solution Part 2:
To calculate the worst case time for block transfer from supervisory to
local processor via the 1771-DCM, add times for the 1771-DCM and local
processor: 15 ms and 31.6 ms, respectively, assuming no other block
transfer modules in the local chassis.
Total Time = 765 ms + 15 ms + 31 ms
= 811 ms
The time required to complete a read or write block transfer depends on
factors that include the number of:
Words of user program
Active I/O channels on the scanner
I/O chassis entries in the rack list for the channel
I/O channels on the scanner that contain block 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)
Typical time required to complete a read or write block transfer depends
on the program scan and the scanner scan as follows:
Time (Read or Write) = Program Scan + 2(Scanner Scan)
Program Scan
The program scan is approximately 2.5 ms per 1K words of user program
when using a mix of examine ON/OFF and block instructions.
Block Transfer with a PLCĆ3
Supervisory Processor