Rockwell Automation 1771-DCM USER MANUAL 1771-DCM - Manual (Page 42)

Calculating Transfer Time
Chapter 7
7Ć8
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 ChassisĆ1
in Rack List
x 9 ms
PLCĆ3 Example Computation
As an example, we will compute the read or write block transfer time
between the supervisory processor and a 1771-DCM 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:
User program contains 20K words.
Channel 1 contains four I/O chassis, with a total of three block transfer
modules including one 1771-DCM.
Channel 2 contains two I/O chassis with no block transfer modules.
Channel 3 contains two I/O chassis with one 1771-DCM.
Channel 4 is made inactive through processor LIST.
You can compute the read or write block transfer times for the supervisory
processor in this example in four steps. Each of the following steps is
explained by an accompanying figure:
1. Diagram the I/O channels of your PLC system (Figure 7.1), showing
the number of:
Block transfer modules in each I/O chassis
Block transfer I/O channels
I/O chassis entries in the rack list for each block transfer I/O
channel
Active I/O channels per scanner
A block transfer I/O channel is a channel that contains one or more
block transfer modules located in any chassis connected to the
channel.