Allen-Bradley ControlLogix System 1756-L1 User Manual page 331

Read or Write Data To or
From Multiple Block
Transfer Modules
Data from a
BT module
Word 1
Input data from
Word 2
the first BT
module
Word 3
Word 1
Word 2
Input data from
Word 3
the next BT
module
Word 4
Word 5
Allen-Bradley HMIs
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
Buffer of INTs
BT_int_buffer_read[0]
BT_int_buffer_read[1]
BT_int_buffer_read[2]
3
BT_int_buffer_read[0]
BT_int_buffer_read[1]
BT_int_buffer_read[2]
BT_int_buffer_read[3]
BT_int_buffer_read[4]
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.
Communicate Over a Remote I/O Network
2
DINTs for use in
the project
BT_input[0,0]
BT_input[0,1]
BT_input[0,2]
BT_input[0,3]
4
BT_input[0,4]
BT_input[1,0]
BT_input[1,1]
BT_input[1,2]
BT_input[1,3]
BT_input[1,4]
Publication 1756-UM001E-EN-P - August 2002
20-15
Input data that is
allocated for the
first BT module
Input data that is
allocated for the
next BT module