Rockwell Automation 1772-LP3 PLC - 2/30 Programmable Controller Programming and Operations Manual User Manual

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Block Transfer

Chapter 10

10Ć2

Figure 10.1

Module PositionĆImage Table Byte Relationship

ЙЙЙЙЙЙ

Output Image Table

17 10 07 00 010

012

017

Output Image

Table Word,

Lower Byte

Control Byte

ЙЙЙЙЙЙ

Input Image Table

110

112

117

Status Byte

Input Image

Table Word,

Lower Byte

Data Table

Bit Numbers

Block

Transfer

Module

Lower

Slot

Upper

Slot

The lower byte of the I/O image table words are used when the

module is in the lower slot and vice versa.

I/O Rack

The block transfer read or write operation (Figure 10.2) is initiated in the
program scan and completed in the I/O scan as follows:

1. Program scan – When the rung goes true, the instruction is enabled.

The number of words to be transferred and the read or write bit that
controls the direction of transfer are set by a bit pattern in the output
image table byte.

2. I/O scan – The processor requests a transfer by sending the output

image table byte data to the block transfer module during the scan of
the output image table. The module signals that it is ready to transfer.
The processor then interrupts the I/O scan and scans the timer/counter
accumulated area of the data table, looking for the address of the
module that is ready to transfer. The module address is stored in BCD
at a word address in the same manner as an accumulated value of a
timer is stored. The module address was entered by the programmer
when entering the block instruction parameters. The word address at
which the module address is stored is called the data address of the
instruction.