MC68HC908GR4MP datasheet(55/286 Pages) FREESCALE

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MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7

Freescale Semiconductor

Chapter 5

Analog-to-Digital Converter (ADC)

5.1 Introduction

This section describes the 8-bit analog-to-digital converter (ADC).

For further information regarding analog-to-digital converters on Freescale microcontrollers, please

consult the HC08 ADC Reference Manual, ADCRM/AD.

5.2 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

5.3 Functional Description

The ADC provides six pins for sampling external sources at pins PTB5/ATD5–PTB0/ATD0. An analog

multiplexer allows the single ADC converter to select one of six ADC channels as ADC voltage in (VADIN).

VADIN 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 5-1.

5.3.1 ADC Port I/O Pins

PTB5/ATD5–PTB0/ATD0 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

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 if the corresponding DDR bit is a 0. If the DDR bit is a 1, the value in the port data latch

is read.

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