MC908KX2MDWE Datasheet, PDF (39/210 Pages) Freescale Semiconductor, Inc – High-performance M68HC08 architecture, Fully upward-compatible object code with M6805, M146805, and M68HC05 Families

Chapter 3
Analog-to-Digital Converter (ADC)
3.1 Introduction
This section describes the 8-bit analog-to-digital converter (ADC).
3.2 Features
Features of the ADC module include:
• Four 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
The ADC provides four pins for sampling external sources at pins PTB3–PTB0. An analog multiplexer
allows the single ADC converter to select one of four 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.
The MC68HC908KX8 uses V_DD as the high voltage reference.
3.3.1 ADC Port I/O Pins
PTB3–PTB0 are general-purpose input/output (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 effect 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 0. If the DDR bit is at 1, the value
in the port data latch is read.
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
Freescale Semiconductor
39