Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS - Manual (Page 176)

Chapter 8
8Ć15
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
scanning sequence list count the module once each time the chassis
appears in the list)
Typical time required for the module to complete a read/write
(bidirectional) block transfer depends on the program scan and the I/O
scan as follows:
time (read/write) = program scan + 2 (I/O scan)
Program Scan
The program scan is approximately 2.5ms per 1K words of user program
when using examine on/off and block instructions.
I/O Scan
The time required for the scanner to complete a read or write block
transfer depends on the number of other block-transfer modules on the
same scanner channel that the program enable simultaneously. Use the
following procedure to calculate the time required for the PLC-3
processor to perform all block transfers on the channel and be ready to
perform the first transfer again.
Block transfer times typically are similar regardless of the type of block
transfer module, whether a read or write operation, or the number of
words transferred. To calculate the I/O scan time for block transfer,
follow these steps:
1. Determine the number of active I/O channels on the scanner.
2. Determine the number of I/O channels with block-transfer modules.
3. Use this table to determine the nominal block transfer time using the
number from steps 1 and 2.