Block transfer, Using block transfers – Rockwell Automation 2706-MB1 MESSAGEVIEW 421 SOFTWARE MANUAL User Manual
Page 106
5–17
Communications Overview
Publication 2706-817
The RIO interface on the MessageView RIO daughterboard supports
the transfer of blocks of data between a PLC and a MessageView
421 terminal.
Note: Some logic controllers do not support block transfer. Check
the user manual for the controller used in the system.
Using Block Transfers
Block transfers are assigned to a single byte of input data (module
control byte) and output data (module status byte) within the rack
assigned to the terminal. These two bytes control the operation of the
block transfer and are no longer available for discrete I/O.
These bytes always occupy the low byte of the lowest module group
in the terminal rack assignment. For example, if the starting module
group is 0:
Rack 03
MessageView I/O
0
2
4
6
1
3
5
7
0
1
2
3
4
5
6
1
0
11
12
13
14
15
16
17
0
1
2
3
4
5
6
1
0
11
12
13
14
15
16
17
Starting Module
Group 0
Input Word
Output Word
Status Byte
Module Control Byte
7
7
No matter how many block transfers are assigned (1 to 10), one byte
is reserved in the input and and one in the output rack.
Note: Two copies of the worksheet in Appendix H are used for
Discrete I/O (input and output). Be sure to block off the status byte
and module control byte in these worksheets if the application uses
block transfer.
Block transfer directions are in reference to the PLC:
•
Block Transfer Reads (BTR) are inputs to the PLC. They are used
to transfer data from data entry variables on the MessageView
terminal.
•
Block Transfer Writes (BTW) are outputs from the PLC. They are
used to transfer data to data display variables on the
MessageView terminal.
Block Transfer