Rabbit eDisplay, User Manual

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24 eDisplay (OP7200)
3.4 Analog Features (OP7200 only)
The single A/D converter used in the OP7200 (the OP7210 does not have analog or touch-
screen capabilities) has a resolution of 11 bits (single-ended mode) or 12 bits (differential
mode). There are eight channels of A/D conversion, and the OP7200 also has provision
for up to four digital inputs. Three of the four digital inputs are available on screw terminal
header J2. The fourth digital input serves as a board status bit, and is controlled by a 0
Ω
surface-mount resistor R159. The factory default is for R159 to not be installed, which
leaves this fourth input pulled up to Vcc.
3.4.1 A/D Converter Inputs
Figure 11 shows a pair of A/D converter input circuits. Each A/D converter input consists
of resistors and a capacitor. The resistors form a10:1 attenuator, and the capacitor protects
the A/D converter input against electrostatic discharges.
Figure 11. A/D Converter Inputs
180 k W
AIN0
AGND
+ V
AIN1
ADC
Factory
Default
2.048 V
0 W
180 k W
1 nF
20 k
W
20 k
W
1 nF
ADC