Rabbit OP7100 User Manual download pdf (Page 146)

140 eDisplay (OP7200)

B.1.1 Power for Analog Circuits

Power to the analog circuits is provided by way of a single-stage low-pass filter, which

isolates the analog section from digital noise generated by the other components. The ana-

log power voltage +V powers the A/D converter chip, the touchscreen controller, and the

reference circuit. The maximum current draw on +V is less than 10 mA. +V is not acces-

sible to the user.

B.1.2 Grounds

There are three grounds, one digital ground on screw-terminal headers J3 (pin 12) and J10

(pin 12), and an analog ground on screw-terminal header J2 (pin 12). The digital and ana-

log grounds share a single split ground plane on the printed-circuit board. Keeping the

grounds separate isolates the noise of the digital section from the analog circuits, provid-

ing for improved performance of the A/D converter chip and the touchscreen controller.

The analog ground is connected at a single point to the digital ground by a single copper

bridge to eliminate the possibility of ground loops. Analog ground should be used as the

return path for inputs connected to the A/D converter chip via pins 4–11 of screw-terminal

header J2.

B.1.3 RabbitNet Power Supplies

There is no provision on the OP7200 to supply power to any RabbitNet peripheral cards

that together with the OP7200 make up a RabbitNet LAN.

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Rabbit OP7100 User Manual Page 146