Rockwell Automation 1771-DCM USER MANUAL 1771-DCM - Manual (Page 35)

Chapter
7
7Ć1
Calculating Transfer Time
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
The time required for the supervisory processor to communicate with the
1771-DCM depends on whether you select discrete data transfer (up to
eight words) or block transfer (up to 64 words), the number of other
remote I/O chassis, and the number of block transfer modules in the local
and remote I/O systems.
You select the mode of transfer between the supervisory processor and the
1771-DCM as either discrete data transfer or block transfer. Discrete data
transfer is faster than block transfer.
Calculate the transfer time between processors when the 1771-DCM is
transferring discrete data by calculating the times associated with the
supervisory processor, 1771-DCM, and the local processor. Assume the
supervisory and local processor systems contain no other block transfer
modules.
Supervisory Processor
The supervisory processor reads discrete input data or writes discrete
output data to/from its I/O through its remote I/O scanner. Calculate the
total scan time of the supervisory processor as the sum of the program
scan, processor I/O scan if applicable, and the remote I/O scan using
values in the table as follows:
Scan PLCĆ2/30 PLCĆ3
Program 5 ms/K Words 2.5 ms/K Words
Processor I/O 0.5 ms/Rack N/A
Remote I/O 7 ms/Chassis 6 ms/Chassis
Calculating Transfer Time
Discrete Transfer Time