Rockwell Automation 1771-DCM USER MANUAL 1771-DCM - Manual (Page 38)

Calculating Transfer Time
Chapter 7
7Ć4
W = Number of Words Transferred
Scan = Program Scan + I/O Scan + (Multiplier) x (Number of Words
Transferred)
= (15 ms)(2) + 1 ms + (0.08)(8) ms
= 30 ms + 1 ms + 0.64 ms
= 31.6 ms
Transfer Time = Supervisory + 1771-DCM + Local
= 82.5 ms + 15 ms + 31.6 ms
= 129 ms
Solution Part 2:
Additional time for two block transfer modules in the local chassis:
Time (PLC-2/05) = 2(0.08 ms) x (Number of Words Transferred)
= 2(0.08 ms)(64) 1
= 10.2 ms
Total Transfer Time = Discrete Transfer + Block Transfer
= 129 ms + 10.2 ms
= 139 ms (Worst Case)
When you select block transfer as the mode of transfer between the
supervisory processor and 1771-DCM, you can transfer up to 64 words
but the transfer time increases.
The time required for the transfer of data from supervisory to local
processor (and vice versa) is the sum of three events:
Supervisory Processor and Remote I/O Scan Time
Transfer Time through the 1771-DCM
Local Processor Scan Time
1771ĆDCM and Local Processor
Refer to Discrete Data Transfer, above, for the time required by the
1771-DCM and the local processor. These times are the same for either
method of transfer between the supervisory processor and the 1771-DCM.
Block Transfer Time