Freescale-semiconductor ColdFire MCF52210 Instrukcja Użytkownika Pobierz pdf (Strona 473)

100

101

Analog-to-Digital Converter (ADC)

MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2

Freescale Semiconductor 26-37

Figure 26-27. ADC Clock Resynchronization for

Non-Simultaneous Parallel Modes

26.5.10 Voltage Reference Pins V

REFH

and V

REFL

The voltage difference between V

REFH

and V

REFL

provides the reference voltage that all analog inputs are

measured against. The reference voltage should be provided from a low noise filtered source capable of

providing up to 1mA of reference current.

Figure 26-28. ADC Voltage Reference Circuit

When tying V

REFH

to the same potential as V

DDA,

relative measurements are being made with respect to

the amplitude of V

DDA

. It is imperative that special precautions be taken to assure the voltage applied to

START0

Asserted

System Clock

Old ADC Clock

ADC Clock After

Resynchronization

ADCA Scan

ADCB Scan

ADCB Scan Start

ADCB Scan Should Start Here

START1 Asserted

ADC Conversion Clock Resynchronized

ADCA Scan Start

Delay in start because ADC Clock cannot

be resynchronized: 5 System Clocks

Wait for next rising

edge of ADC

Conversion Clock

REFH

External

Reference

Voltage

0.1µF

REFL

1.0mH

SEL_VREFL

REFH

to ADC

REFL

to ADC

SEL_VREFH

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