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Table B-2. Positive A/D Converter Input Voltage Ranges
Min. Voltage
(V)
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Other possible ranges are possible by physically changing the resistor values that make up
the attenuator circuit.
It is also possible to read a negative voltage on ADC_IN0 to ADC_IN5 by moving the
jumper (see Figure B-5) on header JP7, JP6, or JP5 associated with the A/D converter
input from analog ground to VREF, the reference voltage generated and buffered by the
A/D converter. Adjacent input channels are paired so that moving a particular jumper
changes both of the paired channels. At the present time Rabbit does not offer the software
drivers to work with single-ended negative voltages, but the differential mode described
below may be used to measure negative voltages.
NOTE: THERM_IN7 was configured to illustrate the use of a thermistor with the sample
program, and so is not available for use as a differential input. There is also no resistor
attenuator for THERM_IN7, so its input voltage range is limited.
Differential measurements require two channels. As the name differential implies, the dif-
ference in voltage between the two adjacent channels is measured rather than the differ-
ence between the input and analog ground. Voltage measurements taken in differential
mode have a resolution of 12 bits, with the 12th bit indicating whether the difference is
positive or negative.
The A/D converter chip can only accept positive voltages. Both differential inputs must be
referenced to analog ground, and both inputs must be positive with respect to analog
ground. Table B-3 provides the differential voltage ranges for this setup.
RabbitCore RCM3700 User's Manual
Amplifier
Max. Voltage
(V)
Gain
+20.0
+10.0
+5.0
+4.0
+2.5
+2.0
10
+1.25
16
+1.0
20
mV per Count
1
10
2
5
4
2.5
5
2.0
8
1.25
1.0
0.625
0.500
99
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