Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 171)

ASCII Module
PLC-2 Family Processors
Appendix A
AĆ3
020
10
Initialization bit tells module up to 4
200
17
020
02
initialization words follow command words
Initialization: Turns off 1st rung except
for first scan at power-up
END 00464
All communication between the ASCII module and the PC processor data
table is controlled by program logic using block transfer programming.
The Mini-PLC-2/15 and PLC-2/30 programmable controllers use block
transfer instructions. The PLC-2/20 uses multiple get instructions for
programming block transfer. Refer to the July 1982 or later edition of the
Programming and Operations Manual for the Mini-PLC-2/15 or PLC-2/30
for a detailed description of block transfer. These are publications
1772-804 and 1772-806 respectively.
The remainder of this section describes block transfer concepts for
programming the ASCII module using the block instructions of the
Mini-PLC-2/15 and PLC-2/30 programmable controllers.
Bidirectional Block Transfer
Bidirectional block transfer is the performance of alternating read and
write operations. A read operation transfers data from the module to the
processor data table. A write operation transfers data from the data table
to the module. User program logic contains the block transfer read
instruction and block transfer write instruction. The format of these block
instructions and definitions of terms are shown in Figure A.2.
Block Transfer Programming