MC68HC908AS32A Datasheet, PDF (59/280 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 3
Analog-to-Digital Converter (ADC)
3.1 Introduction
This section describes the analog-to-digital converter (ADC). The ADC is an 8-bit analog-to-digital
converter.
For further information regarding analog-to-digital converters on Freescale microcontrollers, please
consult the HC08 ADC Reference Manual, Freescale document order number ADCRM/AD.
3.2 Features
Features include:
• 15 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
Fifteen ADC channels are available for sampling external sources at pins
PTD6/ATD14/TACLK–PTD0/ATD8 and PTB7/ATD7–PTB0/ATD0. An analog multiplexer allows the
single ADC converter to select one of 15 ADC channels as ADC voltage in (ADCVIN). ADCVIN is
converted by the successive approximation register-based counters. When the conversion is completed,
ADC places the result in the ADC data register and sets a flag or generates an interrupt. See Figure 3-2.
3.3.1 ADC Port I/O Pins
PTD6/ATD14/TACLK–PTD0/ATD8 and PTB7/ATD7–PTB0/ATD0 are general- purpose I/O pins that
share with the ADC channels.
The channel select bits define which ADC channel/port pin will be used as the input signal. The ADC
overrides the port I/O logic by forcing that pin as input to the ADC. The remaining ADC channels/port pins
are controlled by the port I/O logic and can be used as general-purpose I/O. Writes to the port register or
DDR will not have any affect on the port pin that is selected by the ADC. Read of a port pin which is in
use by the ADC will return a 0 if the corresponding DDR bit is at 0. If the DDR bit is at 1, the value in the
port data latch is read.
NOTE
Do not use ADC channels ATD14 or ATD12 when using the
PTD6/ATD14/TACLK or PTD4/ATD12/TBCLK pins as the clock inputs for
the 16-bit timers.
MC68HC908AS32A Data Sheet, Rev. 2.0
Freescale Semiconductor
59