Siemens simatic s7-400 FM 450-1 User Manual page 78

Modes, settings, parameters and commands
8.12 Initiating a process interrupt
Boundary conditions
If you assign the behavior of the digital outputs, you must observe the following boundary
conditions.
If ...
... you want to assign parameters for the output to
be "active between the comparison value and the
overflow or underflow" ...
...you want to assign the parameters for the
output to be "active for the pulse duration in the
up counting direction"...
...you want to assign the parameters for the
output to be "active for the pulse duration in the
down counting direction"...
Disabling the outputs
The outputs are disabled by the following events, irrespective of the parameter assignment:
● Module watchdog timeout (internal error)
● Removal of the enable bit (CTRL_DQ0 for Q0 and CTRL_DQ1 for Q1 in the DB, see
section "Assignment of the DB (Page 103)")
Default setting
The outputs are disabled in the default setting.
78
then...
...you must ensure that the time between the
events is longer than the minimum operating time
of the outputs (operating time: 300°µs); otherwise
the control pulses at the outputs are lost.
If the counter status again reaches the
comparison value while the output is still active,
no new pulse will be initiated. A further pulse can
only be initiated when the output is no longer
active.
... you must not enable a hardware interrupt when
"the comparison value 1 or 2 in the down
direction is reached".
...you must not enable a hardware interrupt when
"the comparison value 1 or 2 in the up direction is
reached".
Manual, 02/2014, A5E03648739-02
Counter module FM 450-1