MC68HC908GR8A_07 Datasheet, PDF (47/260 Pages) Freescale Semiconductor, Inc – Microcontrollers

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:
• Six channels with multiplexed input
• Linear successive approximation with monotonicity
• 8-bit resolution
• Single or continuous conversion
• Conversion complete flag or conversion complete interrupt
• Selectable ADC clock
3.3 Functional Description
The ADC provides six pins for sampling external sources at pins PTB5/AD5–PTB0/KBD0. An analog
multiplexer allows the single ADC converter to select one of six ADC channels as ADC voltage in (V_ADIN).
V_ADIN is converted by the successive approximation register-based analog-to-digital converter. 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
PTB5/AD5–PTB0/KBD0 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 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
data direction register (DDR) will not have any affect on the port pin that is selected by the ADC. Read of
a port pin in use by the ADC will return a 0.
MC68HC908GR8A • MC68HC908GR4A Data Sheet, Rev. 5
Freescale Semiconductor
47