Allen-Bradley controllogix 1756-L63, User Manual

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Publication 1756-UM001E-EN-P - August 2002
9-12 Communicate with 1771 I/O Over a ControlNet™ Network
Read or Write Data To or
From Multiple Block
Transfer Modules
Use this procedure to program a single MSG instruction to read data
from multiple block transfer modules.
The following diagram shows the flow of data for a block transfer
read. The block transfer write sequence works in the opposite order.
1. The MSG instruction reads 16-bit integers (INTs) from the first
BT module and stores them in a temporary array of INTs.
2. An FAL instruction converts the INTs to 32-bit integers (DINTs).
Logix5000 controllers execute more efficiently and use less
memory when working with DINTs.
3. The MSG instruction reads the next module. This procedures lets
you vary the number of INTs that you read from each module.
4. The FAL instruction moves the data to the next element of
dimension 0 of the DINT array. Each element of this dimension
corresponds to a different BT module.
Data from a
BT module Buffer of INTs DINTs for use in
the project
Input data from
the first BT
module
Word 1
BT_int_buffer_read[0] BT_input[0,0]
Input data that is
allocated for the
first BT module
Word 2
BT_int_buffer_read[1] BT_input[0,1]
Word 3
BT_int_buffer_read[2] BT_input[0,2]
BT_input[0,3]
BT_input[0,4]
Input data from
the next BT
module
Word 1
BT_int_buffer_read[0] BT_input[1,0]
Input data that is
allocated for the
next BT module
Word 2
BT_int_buffer_read[1] BT_input[1,1]
Word 3
BT_int_buffer_read[2] BT_input[1,2]
Word 4
BT_int_buffer_read[3] BT_input[1,3]
Word 5
BT_int_buffer_read[4] BT_input[1,4]
1
2
3 4