Siemens SIMATIC S5 Equipment Manual page 43

R 02/92
Interrupt for several 1P 241 modules on one interrupt line
If several IPs access one interrupt (IRA to IRD), the individual IPs must be identified. For this pur-
pose (up to eight units) a specific bit must be allocated in the peripheral byte O for each 1P; (e.g.,
peripheral bit 0.0 for IP1, peripheral bit 0.1 for IP2 and soon (see section 2.5.2).
If, for example, the peripheral bit 0.0 = 1, the 1P to which this bit was allocated has triggered this
interrupt.
(PER: WST)
When an interrupt occurs, the pertaining interrupt OB is called. The call for function block FB 157
the parameter assignment BEF = KB is written into this organization block.
with
After the call by the interrupt OB, parameter ST shows from which channel the interrupt originated
(i.e., you can have your specific interrupt program processed then).
If during processing of function block FB 157 in the cyclic program an
interrupt occurs, the roup interrupt at the bus is cancelled by FB 157
(or by reading byte 7.
Consequently, no interrupt identity bit can be evaluated in the alarm OB.
In the function block, howeve~ the control bits are updated, so that
depending on the interrupt identifier bits saved in the flag! your specific
interrupt rogram can be called. This means the information about the
channel rom which the interrupt originated is stored in the control
byte (ST).
Therefore after each call of FB 157 in the cyclic program both IP 241
interrupt bits must be scanned!
After having been evaluated, the control bits in the interru t–OB must
be reset, as otherwise the interrupt programs (FBxx and Byy) might
be processed in the cyclic program once again.
This is taken into account in the example in section 2.3.
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Operating Instructions
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