Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE User Manual
Page 230
ASCII Module
For PLCĆ3 Processor
Appendix B
B-8
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 numbers from steps 1 and 2.
Channels with
Block Transfer
Modules
1 Active
Channel
2 Active
Channels
3 Active
Channels
4 Active
Channels
1
2
3
4
40
Ć
Ć
Ć
52
67
Ć
Ć
54
68
98
Ć
58
76
99
123
Block transfer times typically are similar regardless of the type of
block transfer module or the number of words transferred. Nominal
read block transfer times typically are faster than nominal write block
transfer times by approximately 10ms. In this example, consider
them the same.
4.
Count the number of block transfer modules on the channel. If a
chassis containing block transfer modules is repeated in the rack
list, count chassis and modules as often as listed.
5.
Count the number of I/O chassis entries in the rack list for the
channel.
6.
Calculate the block transfer time for the scanner as follows:
Scanner Time =
Nominal
Time
x
# BT modules
on the channel +
#I/O chassis
in rack list
-1
X 9ms
PLC-3 Example Computation
As an example, we will compute the read or write block transfer time
between the supervisory processor and an ASCII module in an I/O
channel with no other block transfer modules, and in an I/O channel
with two other block transfer modules in the following system: