Siemens SIMATIC S5-90U System Manual page 132

Addressing and Access to I/Os
The following Figure illustrates the procedures for direct and indirect I/O access.
PLC
Cyclic Program
Process input
image (PII)
OB1: Cyclic program
Read value from PII
L IW x
Read value direct from
onboard I/Os
L PW x
Write value direct to onboard
I/Os
T PW x
Write value to PIQ
T QW x
Process output
image (PIQ)
Figure 6-11. Procedure for Direct/Indirect I/O Access During Cyclic Program Execution
6-12
Read data
ACCU 1
AKKU 1
ACCU 1
Read data
ACCU 1 Write data to outputs
ACCU 1
Write data to outputs
S5-90U/S5-95U
Onboard External
I/Os I/Os
EWA 4NEB 812 6115-02b