Advanced instruction set chapter 6 – Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations User Manual

Page 93

Advanced Instruction Set

Chapter 6

6Ć36

Figure 6.14

Image Table Byte Relationship vs Module Position

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Data Table

Bit Numbers

10 07

17 00

Output Image Table

Control Byte

Input Image Table

Status Byte

010

012

017

110

112

117

Output Image

Table Word,

Lower Byte

Input Image

Table Word,

Lower Byte

I/O Rack

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.

10154-I

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

Program Scan - When the rung goes true, the instruction is enabled. The
number of words to be transferred by the read or write bit that controls the
direction of transfer are set by a bit pattern in the output image table byte.

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. See
Table 6.C.)

Once the module address is found, the processor locates the address of the file
to which (or from which) the data will be transferred. The file address is stored
in BCD at an address 1008 above the address containing the module address.
This is done in the same manner that the processor locates the preset value of a
timer in a word address 1008 above the accumulated value address.