Rainbow-electronics ATmega103L Manual de usuario descargar pdf (Pagina 71)

ATmega603/103

ADC Data Register - ADCL and ADCH

When an ADC conversion is complete, the result is found in these two registers. It is essential that both registers are read,

and that ADCL is read before ADCH.

ADC Noise Canceling Techniques

Digital circuitry inside and outside the ATmega603/103 generates EMI which might affect the accuracy of analog measure-

ments. If conversion accuracy is critical, the noise level can be reduced by applying the following techniques:

1. The analog part of the ATmega603/103 and all analog components in the application should have a separate ana-

log ground plane on the PCB. This ground plane is connected to the digital ground plane via a single point on the

PCB.

2. Keep analog signal paths as short as possible. Make sure analog tracks run over the analog ground plane, and keep

them well away from high-speed switching digital tracks.

3. The AV

pin on the ATmega603/103 should have its own decoupling capacitor as shown in Figure 49.

4. Use the ADC noise canceler function to reduce induced noise from the CPU.

5. If some Port F pins are used as digital inputs, it is essential that these do not switch while a conversion is in

progress.

Figure 49. ADC Power Connections

Bit 151413121110 9 8

$05 ($25) - - - - - - ADC9 ADC8 ADCH

$04 ($24) ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL

76543210

Read/WriteRRRRRRRR

RRRRRRRR

Initial value00000000

00000000

VCC

GND

10nF

Analog Ground Plane

ATmega603/103

(ADC0) PF0

(ADC7) PF7

(ADC1) PF1

(ADC2) PF2

(ADC3) PF3

(ADC4) PF4

(ADC5) PF5

(ADC6) PF6

AREF

AGND

AVCC

6161

6262

6363

6464

PEN

(AD0) PA0

1 2 ... 66 67 68 69 70 71 72 73 74 75 76 ... 125 126

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Rainbow-electronics ATmega103L Manual de usuario Pagina 71

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