Siemens Simatic S5-101U - Page 7

Task: When input I 0.0 becomes "l",
outputs Q @.g. .. Q 0.7 are to assume
the state of flags F
3.a ... F3.7. In
order to keep the response time as
short and constant as possible,
ten
interrupt scans should be written in
the user program.
User
program
STEP
5 program (STL)
Interrupt
routine
Expl
anat ions
1st interrupt scan: by loading PB
0,
I 0.0 is scanned direct, i.e. by-
passing the process image, and mapped
on F
@.a.
If F 0.0 (and consequently
I 0.0)
is "l", a jump is made to the
interrupt routine.
F 10.0 defines the
return address.
2nd
i nterrupt scan
10th interrupt scan
Flag byte FB3 is transferred direct into
peripheral byte PB
0, i.e. direct to
the outputs. The process output image
is updated.
By scanning flags
F 10.0 ... F 11.0 (only
one flag is used), the user program is
continued at the return address last
defined.
Fig.
6: Example of a user program with interrupt scanning