Siemens SIMATIC S5-90U System Manual page 283

S5-90U/S5-95U
Example: An electronic transducer is connected to interrupt input I 34.0. When the
transducer initiates an interrupt, the program branches to FB3.
STL
OB3
A I 35.4
R I 35.4
JC FB3
.
.
.
BE
Caution
!
Be sure to save the flags of the cyclic program (into a data block for example) if these
flags are overwritten during interrupt processing and are needed in the cycle again.
Please note the following:
• After interrupt processing, the interrupt bits in the diagnostic byte must be reset to "0" by the
program (see Table 10-4).
• The operating system always updates the diagnostic byte prior to calling OB3.
• Any causes of interrupt occurring during OB3 processing are not entered in the diagnostic byte.
The operating system enters them in the diagnostic byte prior to the next OB3 call.
• The internal timers are not updated during interrupt processing.
• During interrupt processing with the OB3, data can only be transferred to the onboard I/Os.
The data is transferred directly to the relevant onboard outputs by means of the T PY/PW
operation. The "normal" PIQ is updated. Neither an interrupt PII nor an interrupt PIQ are used.
Table 10-5. Transfer Operations to the Onboard Outputs
STEP 5 Operations for
S5-95U S5-90U
T PY 32/33 T PY 32/33
T PW 32/40 T PW 32
EWA 4NEB 812 6115-02b
Table 10-4. Program Example Including OB3
There was an interrupt at I 34.0.
Bit 4 in the diagnostic byte is reset to "0".
The interrupt reaction program in FB3 is
executed.
The contents of ACCU1 are written directly to the onboard
outputs and into the normal PIQ.
Onboard Interrupt Inputs
Explanation
Explanation
10-3