Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 98)

Advanced Instruction Set
Chapter 6
6Ć41
Function: Acts upon false-to-true transitions. When the rung goes:
True
Data is transferred.
False
No action is taken.
Block Transfer Write
Symbol: BLOCK
X-FER 0
Purpose: Writing information from the processor’s output image table to the
1771 I/O module in one I/O scan.
Syntax: Programmed as an output instruction. This instruction requires two
words of your program.
Function: Acts upon false-to-true transitions when the rung goes:
True
Data is transferred.
False
No action is taken.
The purpose of block transfer data buffering is to allow the data to be validated
before it can be used. Data that is read from the block transfer module and
transferred to data table locations must be buffered. Data that is written to the
module does not need to be buffered because block transfer modules perform
this function internally.
Transferred data is buffered to ensure that both the transfer and the data are
valid. As an example, readings from an open-circuited temperature sensor
(invalid data) could have a valid transfer from an analog input module to the
data table. The processor examines the data-valid bit and/or the diagnostic bit
which is contained in the transferred data to determine whether or not the data is
valid. The block transfer done bit is set if the transfer is valid.
The data-valid bit and/or the diagnostic bit differs for each block transfer
module. Some modules set one or both for the entire file of words transferred,
while others set a data-valid bit or diagnostic bit in each word. Refer to the
Buffering Data