Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 156)

Special Programming Techniques
Chapter 11
11Ć9
WARNING: When programming multiple writes (or reads) to
the same module, programming errors could prevent the desired
transfer from taking place or limit the number of words
transferred. Invalid data could be sent to an analog output device
(or could be operated upon in subsequent scans) resulting in
unpredictable machine operation. Damage to equipment and/or
injury to personnel could occur.
Definitions: Bidirectional block transfer is the sequential performance of block
transfer read and block transfer write operations. The order of operation is
generally determined by the I/O module.
Syntax: Two rungs of our program are required, one containing the block
transfer read instruction, the other containing the block transfer write
instruction. When both instructions are given the same module address, the pair
are considered as bidirectional block transfer instructions.
Operations: Figure 11.3 shows a sample program for using a bidirectional
block transfer technique. Do not enter this sample program using on-line
production equipment.
Figure 11.3
Bidirectional Block Transfer
EN Block XĆFer Read
Data Addr:
Module Addr:
Block Length:
File: 040
130
05
070- 074
DN
1 013
07
113
07
2
Inputs
EN Block XĆFer Write
Data Addr:
Module Addr:
Block Length:
File: 041
130
05
00- 064
DN
1 013
06
113
06
2
Inputs
The operation’s cycle for the above program is similar to the operation’s cycle
using one block transfer instruction. However, understanding your entered
values is essential. Therefore, we will not discuss each part of the instruction.
Bidirectional Block Transfer