Book Analog Interfacing to Embedded Microprocessors
microprocessor starts a conversion and is placed into a wait state until the con-
version is complete. The microprocessor can also start a conversion on any
channel (by reading data from that channel), then wait for the conversion to
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
annaabi.ee 
