Rockwell Automation 57C421B Pulsetach Input Module/DCS 5000/AutoMax - Manual (Page 37)

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4.4 Applying the Module
In order for hardware to be referenced by application software, it is
first necessary to assign symbolic names to the hardware. This is
accomplished in the configuration, as described in the section 4.3.
Each task that wishes to reference the symbolic names assigned to
the Pulsetach Input module may do so by declaring those names
COMMON. Once this has been done, any reference to those
symbolic names within the task will reference the bit or register
defined in the configurations.
The frequency with which tasks read input variables and write output
variables depends on the programming language being used.
Ladder Logic and Control Block tasks read all their inputs once at
the beginning of each scan, regardless of how often the inputs are
referenced in the task and write all output variables at the end of the
scan. BASIC statements (even within Control Block tasks) read an
input each time it is referenced and write an output each time it is
referenced.
4.4.1 Speed Mode Example
The following is an example of a Control Block task that handles
interrupts from the module. All variables declared as COMMON are
assumed to be previously been defined during configuration.
In the example below, the module is continuously accumulating
pulses from a pulsetach. The module is set up to capture the value
of the counter at a periodic rate and then generate an interrupt. This
task could be used to read in counts and then accumulate them in
software. It could also be used to generate a velocity signal (dx/dt).
1 !ă
2 !ăSPEED MODE EXAMPLE
3 !ăTASKNAME : PG_SPEED
4 !ăPRIORITY : 5
5 !ă
1000 COMMON TIMER% \!Counter read time
1005 COMMON ISCR% \!Interrupt and status register
1010 COMMON COUNT% \!Counter data
1015 COMMON MULT@ \!Pulse multiplier
1020 COMMON CCLK_EN@ \!CCLK enable
1025 COMMON INT_R@ \! Timer interrupt enable
1200 LOCAL COUNTER_VALUE% \!Counter value from buffer
2100 MULT@ = ON \!Pulse multiplier times 4
2200 TIMER% = 99 \!Read every 50 milliseconds
2201 !
2202 ! Set all other timers in the rack here.
2203 ! (To be done in only 1 task in a rack.)
2204 !
3000 !ă
3001 !ăThe following statement connects the name COUNTER_EVENT
3002 !ăto the interrupt defined in ISCR%. The event name should
3003 !ăbe as descriptive as possible. The watchdog timeout has
3004 !ăbeen set to 12 Processor clock ticks (12*5.5 secs). If the time
3005 !ăbetween interrupts exceeds this value, a severe error
3006 !ăwill be declared and the system will be stopped. For
3007 !ă
3008 !ă
3009 !ă
3010 EVENT NAME=COUNTER_EVENT, INTERRUPT_STATUS=ISCR%,
TIMEOUT=12
4000 !ă
4001 !ăThe following statement enables the constant clock" from
4002 !ăthis module. If there is more than one interrupt task in a
4003 !ăchassis, the task that enables the constant clock" should
4004 !ăalways be the lowest priority task.
4005 !ă
4100 DIS_CRL@=FALSE \!Counter will be reset on interrupt.