Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 171)

Block Transfer
Chapter 14
14-16
Figure 14.7
Programming Multiple Reads from One Module
EN
Block Xfer Read
Data Addr:
Module Addr:
Block Length:
File:
052
141
04
163 DN
014
07
114
07
160Ć
EN
Block Xfer Read
Data Addr:
Module Addr:
Block Length:
File:
052
141
08
167 DN
014
17
114
17
160Ć
1 2 3
Inputs
EN
Block Xfer Read
Data Addr:
Module Addr:
Block Length:
File:
052
141
03
162 DN
014
17
114
17
160Ć
1 2 3
Inputs
11
Input
DN
114
17
2
Input
1 2 3
Inputs
3
Input
You should buffer block transfer data to allow the data to be validated
before it is 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 need not 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 data-valid and/or diagnostic bits
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 and/or diagnostic bits differ for each block transfer module.
Some modules set one or both for the entire file of words transferred, while
others set a data-valid diagnostic bit in each word. See the documentation
for the block transfer module to determine the correct usage of the
diagnostic and/or data valid bit(s).
Buffering Data