Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 227)

ASCII Module
For PLCĆ3 Proessor
Appendix B
B-5
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