Rainbow-electronics ATmega128L Manuel d'utilisateur télécharger pdf (Page 221)

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ATmega128(L)

2467B–09/01

Analog to Digital

Converter

Features • 10-bit Resolution

• 0.5 LSB Integral Non-linearity

• ±2 LSB Absolute Accuracy

• TBD - 260 µs Conversion Time

• Up to TBD kSPS at Maximum Resolution

• 8 Multiplexed Single Ended Input Channels

• 7 Differential Input Channels

• 2 Differential Input Channels with Optional Gain of 10x and 200x

• Optional Left Adjustment for ADC Result Readout

• 0 - VCC ADC Input Voltage Range

• Selectable 2.56 V ADC Reference Voltage

• Free Running or Single Conversion Mode

• Interrupt on ADC Conversion Complete

• Sleep Mode Noise Canceler

The ATmega128 features a 10-bit successive approximation ADC. The ADC is con-

nected to an 8-channel Analog Multiplexer which allows 8 single-ended voltage inputs

constructed from the pins of Port F. The single-ended voltage inputs refer to 0 V (GND).

The device also supports 16 differential voltage input combinations. Two of the differen-

tial inputs (ADC1, ADC0 and ADC3, ADC2) are equipped with a programmable gain

stage, providing amplification steps of 0 dB (1x), 20 dB (10x), or 46 dB (200x) on the dif-

ferential input voltage before the A/D conversion. Seven differential analog input

channels share a common negative terminal (ADC1), while any other ADC input can be

selected as the positive input terminal. If 1x or 10x gain is used, 8-bit resolution can be

expected. If 200x gain is used, 7-bit resolution can be expected.

The ADC contains a Sample and Hold circuit which ensures that the input voltage to the

ADC is held at a constant level during conversion. A block diagram of the ADC is shown

Figure 107.

The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more

than ±0.3 V from V

. See the paragraph “ADC Noise Canceler” on page 227 on how to

connect this pin.

Internal reference voltages of nominally 2.56 V or AV

are provided on-chip. The volt-

age reference may be externally decoupled at the AREF pin by a capacitor for better

noise performance.

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Rainbow-electronics ATmega128L Manuel d'utilisateur Page 221