ATmega16 datasheet(206/315 Pages) ATMEL

206 / 315 page

206

ATmega16(L)

2466E–AVR–10/02

If the user has a fixed voltage source connected to the AREF pin, the user may not use

the other reference voltage options in the application, as they will be shorted to the

external voltage. If no external voltage is applied to the AREF pin, the user may switch

between AVCC and 2.56V as reference selection. The first ADC conversion result after

switching reference voltage source may be inaccurate, and the user is advised to dis-

card this result.

If differential channels are used, the selected reference should not be closer to AVCC

than indicated in Table 121 on page 291.

ADC Noise Canceler

The ADC features a noise canceler that enables conversion during sleep mode to

reduce noise induced from the CPU core and other I/O peripherals. The noise canceler

can be used with ADC Noise Reduction and Idle mode. To make use of this feature, the

following procedure should be used:

Make sure that the ADC is enabled and is not busy converting. Single Con-

version Mode must be selected and the ADC conversion complete interrupt

must be enabled.

Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a con-

version once the CPU has been halted.

If no other interrupts occur before the ADC conversion completes, the ADC

interrupt will wake up the CPU and execute the ADC Conversion Complete

interrupt routine. If another interrupt wakes up the CPU before the ADC con-

version is complete, that interrupt will be executed, and an ADC Conversion

Complete interrupt request will be generated when the ADC conversion

completes. The CPU will remain in active mode until a new sleep command

is executed.

Note that the ADC will not be automatically turned off when entering other sleep modes

than Idle mode and ADC Noise Reduction mode. The user is advised to write zero to

ADEN before entering such sleep modes to avoid excessive power consumption. If the

ADC is enabled in such sleep modes and the user wants to perform differential conver-

sions, the user is advised to switch the ADC off and on after waking up from sleep to

prompt an extended conversion to get a valid result.

Analog Input Circuitry

The Analog Input Circuitry for single ended channels is illustrated in Figure 105. An ana-

log source applied to ADCn is subjected to the pin capacitance and input leakage of that

pin, regardless of whether that channel is selected as input for the ADC. When the chan-

nel is selected, the source must drive the S/H capacitor through the series resistance

(combined resistance in the input path).

The ADC is optimized for analog signals with an output impedance of approximately

10 k

Ω or less. If such a source is used, the sampling time will be negligible. If a source

with higher impedance is used, the sampling time will depend on how long time the

source needs to charge the S/H capacitor, with can vary widely. The user is recom-

mended to only use low impedant sources with slowly varying signals, since this

minimizes the required charge transfer to the S/H capacitor.

If differential gain channels are used, the input circuitry looks somewhat different,

although source impedances of a few hundred k

Ω or less is recommended.

Signal components higher than the Nyquist frequency (f

ADC/2) should not be present for

either kind of channels, to avoid distortion from unpredictable signal convolution. The

user is advised to remove high frequency components with a low-pass filter before

applying the signals as inputs to the ADC.

ATMEGA16 датащи(PDF) 206 Page - ATMEL Corporation

ATMEGA16 датащи(HTML) 206 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL