MC68HC908AT32 Datasheet, PDF (225/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 21
Analog-to-Digital Converter (ADC-8)
NOTE
This analog-to-digital converter is for the CAN (64-pin QFP) protocol only.
21.1 Introduction
This section describes the analog-to-digital converter (ADC-8). The ADC is an 8-bit analog-to-digital
converter.
21.2 Features
Features of the ADC module include:
• Eight channels with multiplexed input
• Linear successive approximation
• 8-bit resolution
• Single or continuous conversion
• Conversion complete flag or conversion complete interrupt
• Selectable ADC clock
21.3 Functional Description
Eight ADC channels are available for sampling external sources at pins PTB7/ATD7–PTB0/ATD0. An
analog multiplexer allows the single ADC converter to select one of eight ADC channels as ADC voltage
in (ADCVIN). ADCVIN is converted by the successive approximation register-based counters. When the
conversion is completed, the ADC places the result in the ADC data register and sets a flag or generates
an interrupt. See Figure 21-1.
21.3.1 ADC Port I/O Pins
PTB7/ATD7–PTB0/ATD0 are general-purpose I/O pins that are shared 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 logic 0 if the corresponding DDR bit is at logic 0. If the DDR bit is at logic 1,
the value in the port data latch is read.
MC68HC908AT32 Data Sheet, Rev. 3.1
Freescale Semiconductor
225