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Addressing
5.3.1
Accessing the PII
In the "RESTART" mode and at the beginning of program scanning, the digital and analog input
module signal states are written into the PII. The input images of subunit A and subunit B are then
exchanged and compared. Any differences in input information are subjected to discrepancy
analysis to establish whether there is a hardware error in the relevant input module or whether
the deviation is tolerable. A standard value is generated from tolerable input value differences.
This uniform value allows both subunits to execute identically.
The statements in the control program use a particular address to indicate what information is
currently needed. The processor then reads the data that was current at the beginning of program
scanning and works with it.
Reading bit by bit
for binary operations:
Reading byte by byte
for loading into ACCUM 1:
ACCUM 1
Reading word by word
for loading into ACCUM 1:
ACCUM 1
Figure 5-6. Accessing the PII in the Case of Digital Input Modules
5-6
A I 2.2
L IB 12
15
High byte
Low byte
L IW 40
15
High byte
Low byte
PII
7 6 5 4 3 2 1 0
0
0
S5-115F Manual
Bit No.
Byte 2
Byte 12
Byte 40
Byte 41
EWA 4NEB 811 6148-02
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