MC68HC908GR4MP datasheet(58/286 Pages) FREESCALE

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Analog-to-Digital Converter (ADC)

MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7

Freescale Semiconductor

5.6 I/O Signals

The ADC module has six pins shared with port B, PTB5/AD5–PTB0/ATD0.

5.6.1 ADC Analog Power Pin (VDDAD)/ADC Voltage Reference High Pin (VREFH)

The ADC analog portion uses VDDAD as its power pin. Connect the VDDAD pin to the same voltage

potential as VDD. External filtering may be necessary to ensure clean VDDAD for good results.

NOTE

For maximum noise immunity, route VDDAD carefully and place bypass

capacitors as close as possible to the package.

5.6.2 ADC Analog Ground Pin (VSSAD)/ADC Voltage Reference Low Pin (VREFL)

The ADC analog portion uses VSSAD as its ground pin. Connect the VSSAD pin to the same voltage

potential as VSS.

5.6.3 ADC Voltage In (VADIN)

VADIN is the input voltage signal from one of the six ADC channels to the ADC module.

5.7 I/O Registers

These I/O registers control and monitor ADC operation:

•

ADC status and control register (ADSCR)

•

ADC data register (ADR)

•

ADC clock register (ADCLK)

5.7.1 ADC Status and Control Register

Function of the ADC status and control register (ADSCR) is described here.

COCO — Conversions Complete Bit

When the AIEN bit is a logic 0, the COCO is a read-only bit which is set each time a conversion is

completed except in the continuous conversion mode where it is set after the first conversion. This bit

is cleared whenever the ADSCR is written or whenever the ADR is read.

If the AIEN bit is a logic 1, the COCO is a read/write bit which selects the CPU to service the ADC

interrupt request. Reset clears this bit.

1 = Conversion completed (AIEN = 0)

0 = Conversion not completed (AIEN = 0), or CPU interrupt (AIEN = 1)

Address:

$0003C

Bit 7

654321

Bit 0

Read:

COCO

AIEN

ADCO

ADCH4

ADCH3

ADCH2

ADCH1

ADCH0

Write:

Reset:

00011111

Figure 5-2. ADC Status and Control Register (ADSCR)

MC68HC908GR4MP Datasheet(PDF) 58 Page - Freescale Semiconductor, Inc

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