Rabbit RabbitCore RCM4100, User Manual

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90 RabbitCore RCM4100
B.4.3 Analog Features (RCM4100 only)
The Prototyping Board has typical support circuitry installed to complement the ADS7870
A/D converter on the RCM4100 model (the A/D converter is not available on the
RCM4110 and the RCM4120).
B.4.3.1 A/D Converter Inputs
Figure B-6 shows a pair of A/D converter input circuits. The resistors form an approx. 11:1
attenuator, and the capacitor filters noise pulses from the A/D converter input. The 470
Ω
inline jumpers allow other configurations (see Table B-6) and provide digital isolation when
you are not using an A/D converter (Parallel Port D is available). These jumpers optimize
using RabbitCore modules with or without A/D converters—if you are designing your own
circuit, the best performance for the A/D converter would be realized with 0
Ω
resistors.
Figure B-6. A/D Converter Inputs
The A/D converter chip can make either single-ended or differential measurements
depending on the value of the
opmode
parameter in the software function call. Adjacent
A/D converter inputs are paired to make differential measurements. The default setup on
the Prototyping Board is to measure only positive voltages for the ranges listed in Table B-3.
Table B-3. Positive A/D Converter Input Voltage Ranges
Min. Voltage
(V)
Max. Voltage
(with prescaler)
(V)
Gain
Multiplier
A/D Converter
Actual Gain
Resolution
(mV)
0.0 +22.528 ×1 1 11
0.0 +11.264 ×2 1.8 5.5
0.0 +5.632 ×4 3.6 2.75
0.0 +4.506 ×5 4.5 2.20
0.0 +2.816 ×8 7.2 1.375
0.0 +2.253 ×10 9.0 1.100
0.0 +1.408 ×16 14.4 0.688
0.0 +1.126 ×20 18 0.550
100 k W
LN0_IN
AGND
LN1_IN
ADC
BVREF =
2.048 V
100 k W
2.2 nF
10 k
W
10 k
W
2.2 nF
ADC
(RCM4100)
JP23/JP24
1
3
Inline jumpers are
470 W resistors