Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 198)

ASCII Module
PLC-2 Family Processors
Appendix A
AĆ30
Overview
Block transfer is the method by which the PLC–3 processor
communicates with the ASCII module. The PLC–3 controller can
perform read, write, and bidirectional block transfer operations. During a
block transfer read, data is read from the I/O module and is transferred to
PLC–3 controller memory. During a block transfer write, data is
transferred from memory and is written to the I/O module. Bidirectional
block transfer requires both read and write operations. Each operation can
transfer a maximum of 64 words.
Block Transfer Operation
Block transfer instructions use two files when transferring data and
commands between the block transfer module and the PLC–3 processor:
a data file that contains data to be transferred, and a control file that
contains control bits, module location, data table address and length of the
data file (Figure A.11). Communication between module and processor is
directed by the 1775–S4A scanner. Once the instruction is enabled, the
scanner directs the transfer of data to or from the enabled block transfer
module according to the information contained in the instruction’s control
file. Once the instruction is enabled, it automatically sets and resets its
control bits in accordance with the various steps required to execute the
read or write operation.
Block Transfer Programming