Echelon FT 3150 Smart Transceiver - Manual (Page 77)

FT 3120 / FT 3150 Smart Transceiver Data Book 71
Timer/Counter Input Objects
Input timer/counter objects have the advantage (over non-timer/counter objects) in that input events will be captured
even if the application processor is occupied doing something else when the event occurs. A true when statement
condition for an event being measured by a timer/counter is the completion of the measurement and a value
being returned to an event register. If the processor is delayed due to software processing and cannot read the
register before another event occurs, then the value in the register will reflect the status of the last event. The
timer/counters are automatically reset upon completion of a measurement. The first measured value of a
timer/counter is always discarded to eliminate the possibility of a bad measurement after the chip comes
out of a reset condition. Single events can not be measured with the timer/counters. Figure 3.35 shows an
example of how the timer/counter objects are processed with a Neuron C when statement.
Figure 3.35 Example of when Statement Processing Using the Ontime Input Function
Dualslope Input
This input object uses a timer/counter to control and measure the integration periods of a dualslope integrating analog
to digital converter (see Figure 3.36). The timer/counter provides the control output signal and senses a comparator
output signal. The control output signal controls an external analog multiplexer which switches between the unknown
input voltage and a voltage reference. The input pin of the timer/counter is driven by an external comparator which
compares the output of the integrator with a voltage reference. At the end of conversion, the external comparator will
drive a low level to one of pins IO4 – IO7. If external circuitry indicates “end of conversion” with a high level, use
the invert keyword in the I/O declaration.
Example of a
when statement
missing a present
event but evalu-
ating a previous
event
TIME
INPUT
SIGNAL
Example of a
when statement
evaluating true
(unless it is the
first event)
STOP TIMER/COUNTER
SET FLAG LOAD NEW VALUE
INTO REGISTER
START
TIMER/
COUNTER
READ TIMER/COUNTER FLAG AND REGISTER
FROM THE PREVIOUS EVENT
END OF
io_in()
START OF
io_in()
STOP
TIMER/COUNTER
SET FLAG
LOAD EVENT
REGISTER
START
TIMER/
COUNTER
TIME
INPUT
SIGNAL
(event)
t
ret
t
fin
READ
TIMER/
COUNTER
FLAG AND
REGISTER
CLEAR FLAG
END OF
io_in()
START OF
io_in()
(when
statement)
t
ret
t
fin