Rabbit 2000, Getting Started

Page: 26 / 43

Getting Started Manual 21
4.2.4 Analog Input
The analog input channel on the Jackrabbit (AD0 on header J5) works by varying analog
output channel DA0 until its voltage matches the input voltage on AD0. DA0 obviously
cannot be used while an input voltage is being measured, although channel DA0 is still
available. The value returned corresponds to the value that DA0 required to match the
input voltage (you would call
anaOut(0,value)
for DA0 to provide that same voltage).
If the value returned is negative, then the function considers the value suspect for some
reason (most likely a failure of the DA0 voltage to settle quickly). The value can be taken
as is, or another measurement can be done.
void anaIn(int channel, int *value)
Analog input for the Jackrabbit analog input channel (AD0).
jrioInit must be called first.
channel is the input channel number (0 only on the Jackrabbit).
An integer between 0 and 1024 will be returned in
value
, corresponding to a voltage obtained if
output channel DA0 was set to that value. If a value is found, but the voltage has not appeared to
fully settle, the value will be negative (but equal in magnitude to the found voltage) to allow
remeasurement if desired.
See sample program
JRIOTEST.C
for an example of the use of
anaIn
.
Two versions of the analog input function are available: the standard function, listed above, that
does not return until the measurement has been made, and a cofunction version that can be called
from within a costatement. This cofunction version allows other tasks to be performed while the
voltage match is being made. The voltage measurement will take ten calls of the cofunction ver-
sion to make a measurement.
void cof_anaIn(int channel, int *value)
The parameters are identical to those described above for anaIn .
See sample program
JRIO_COF.C
for an example of the use of
cof_anaIn
.
m
V
max
V
min
–
PWM_MAX0 PWM_MIN –
---------------------------------------------------------------------
=
b V
max
m PWM_MAX0
×
– =
voltage m value
×
b + =