Siemens SIMATIC S5-90U System Manual page 180

STEP 5 Operations
Load Operation:
During loading, information is copied from a memory area, e.g., from the PII, into ACCU 1.
The previous contents of ACCU 1 are shifted to ACCU 2.
The original contents of ACCU 2 are lost.
Example: Two consecutive bytes (IB 7 and IB 8) are loaded from the PII into the accumulator.
Loading does not change the PII (see Figure 8-2).
Lost
information
Byte d Byte c
Byte b Byte a
Transfer Operation:
During transfer, information from ACCU 1 is copied into the addressed memory area, e.g., into the
PIQ.
This transfer does not affect the contents of ACCU 1.
When transfer to the digital output area occurs, the byte or word in question in the PIQ is
automatically updated.
Example: Figure 8-3 shows how byte a, the low byte in ACCU 1, is transferred to QB 5.
ACCU 2
Byte d Byte c
Byte d Byte c
8-12
ACCU 2
Byte d Byte c
Byte b Byte a
0 IB 7
Figure 8-2. Execution of the Load Operation
ACCU 1
Byte b Byte a
T QB 5
Byte b Byte a
Figure 8-3. Transferring a Byte
ACCU 1
Byte b Byte a
L IB 7
0 IB 7
L IB 8
0 IB 8
Information Lost
in the PIQ information
Previous value
Byte a
of QB 5
EWA 4NEB 812 6115-02b
S5-90U/S5-95U
Information
from the PII
IB 7
IB 8