MC68HC908LB8_05 Datasheet, PDF (46/234 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Analog-to-Digital Converter (ADC)
3.2 Features
Features of the ADC module include:
• 7 channels with multiplexed input
• Linear successive approximation
• 8-bit resolution
• Single or continuous conversion
• Conversion complete flag or conversion complete interrupt
• Selectable ADC clock
3.3 Functional Description
Seven ADC channels are available for sampling external sources at pins PTB7/ADC6, PTA6/ADC5,
PTA4/ADC4–PTA0/ADC0. An analog multiplexer allows a single ADC converter to select one of seven
ADC channels as ADC voltage in (ADCVIN). ADCVIN is converted by the successive approximation
register based counters. When the conversion is complete, ADC places the result in the ADC data register
and sets a flag or generates an interrupt.
See Figure 3-2.
INTERNAL DATA BUS
READ DDRAx/DDRBx
WRITE DDRAx/DDRBx
RESET
WRITE PTAx/PTBx
READ PTAx/PTBx
DDRAx/DDRAx
PTAx/PTBx
DISABLE
PTAx/PTBx
ADC CHANNEL x
ADC DATA REGISTER
CONVERSION
INTERRUPT
LOGIC
COMPLETE
ADC
DISABLE
ADC
VOLTAGE IN
(V_ADIN)
CHANNEL
SELECT
ADCH[4:0]
AIEN COCO
BUS CLOCK
ADC CLOCK
CLOCK
GENERATOR
ADIV[2:0]
Figure 3-2. ADC Block Diagram
3.3.1 ADC Port I/O Pins
PTB7/ADC6, PTA6/ADC5, PTA4/ADC4–PTA0/ADC0 are general-purpose I/O (input/output) pins that
share with the ADC channels. The channel select bits define which ADC channel/port pin will be used as
MC68HC908LB8 Data Sheet, Rev. 1
46
Freescale Semiconductor