Book Analog Interfacing to Embedded Microprocessors
complete and perform another read to get the result. The AD7824 also pro-
vides an interrupt output that indicates when a conversion is complete.
Internal Microcontroller ADCs
Many microcontrollers contain on-chip ADCs. Typical devices include the
Microchip PIC167C7xx family and the Atmel AT90S4434. Most microcon-
troller ADCs are successive approximation because this gives the best trade-
off between speed and IC real estate on the microcontroller die.
The PIC16C7xx microcontrollers contain an 8-bit successive approxima-
tion ADC with analog input multiplexers. The microcontrollers in this
family have from 4 to 8 channels. Internal registers control which channel is
selected, start of conversion, and so on. Once an input is selected, there is
a settling time that must elapse to allow the S/H capacitor to charge before
the A/D conversion can start. The software must insure that this delay takes
place.
Reference Voltage
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