Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 92)

Advanced Instruction Set
Chapter 6
6Ć35
SECTION E
Block Transfer Instructions
Block transfer refers to a set of instructions and a programming technique used
to transfer many words of data in one I/O scan. You can transfer data either
from intelligent 1771 I/O modules to the processor’s data table or from the
processor’s data table to the intelligent 1771 I/O modules.
There are two types of block transfer instructions:
Block transfer read
Block transfer write
We will discuss these instructions later in this chapter.
These instructions can transfer from 1 to 64 words depending on the particular
type of intelligent I/O module.
The processor uses two I/o image table bytes to communicate with block
transfer modules. The byte corresponding to the module’s address in the output
image table (control byte) contains the read or write bit for initiating the transfer
of data. The byte corresponding to the module’s address in the input image
table (status byte) is used to signal the completion of the transfer.
NOTE: Do not use word 127 for data storage.
Whether the upper or lower byte of the I/O image table word is used depends on
the position of the module in the chassis’ module group. If the module is
installed using a left slot or dual slot then the lower byte is used. Address the
left slot as slot 0, address the upper slot as slot 1 (Figure 6.14).
Introduction
Basic Operation