MC908AZ32ACFUE Datasheet, PDF (229/324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 21
Analog-To-Digital Converter (ADC-15)
21.1 Introduction
This section describes the analog-to-digital converter (ADC-15). The ADC is an 8-bit analog-to-digital
converter.
21.2 Features
Features of the ADC module 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
21.3 Functional Description
Fifteen ADC channels are available for sampling external sources at pins
PTD6/ATD14/TCLK–PTD0/ATD8 and PTB7–PTB0. 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 21-1.
21.3.1 ADC Port I/O Pins
PTD6/ATD14/TCLK–PTD0/ATD8 and PTB7–PTB0 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 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.
NOTE
Do not use ADC channels ATD14 or ATD12 when using the
PTD6/ATD14/TCLK or PTD4/ATD12 pins as the clock inputs for the 16-bit
Timers.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
229