HCS08 datasheet(224/290 Pages) MOTOROLA

224 / 290 page

Analog-to-Digital Converter (ATD) Module

MC9S08GB/GT

224

MOTOROLA

14.2 Signal Description

14.2.1 Overview

The ATD supports eight input channels and requires 4 supply/reference/ground pins. These pins are listed

in Table 14-1.

14.2.1.1 Channel Input Pins — AD7–AD0

The channel pins are used as the analog input pins of the ATD. Each pin is connected to an analog switch

which serves as the signal gate into the sample submodule.

14.2.1.2 ATD Reference Pins — VREFH, VREFL

These pins serve as the source for the high and low reference potentials for the converter. Separation from

the power supply pins accommodates the filtering necessary to achieve the accuracy of which the system

is capable.

14.2.1.3 ATD Supply Pins — VDDAD, VSSAD

These two pins are used to supply power and ground to the analog section of the ATD. Dedicated power

is required to isolate the sensitive analog circuitry from the normal levels of noise present on digital power

supplies.

NOTE:

VDDAD and VDD must be at the same potential. Likewise, VSSAD and VSS must be at

the same potential.

14.3 Functional Description

The ATD uses a successive approximation register (SAR) architecture. The ATD contains all the

necessary elements to perform a single analog-to-digital conversion.

A write to the ATDSC register initiates a new conversion. A write to the ATDC register will interrupt the

current conversion but it will not initiate a new conversion. A write to the ATDPE register will also abort

the current conversion but will not initiate a new conversion. If a conversion is already running when a

write to the ATDSC register is made, it will be aborted and a new one will be started.

Table 14-1 Signal Properties

Name

Function

AD7–AD0

Channel input pins

VREFH

High reference voltage for ATD converter

VREFL

Low reference voltage for ATD converter

VDDAD

ATD power supply voltage

VSSAD

ATD ground supply voltage

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