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Chapter 44 A/D Converter
1.Overview of A/D Converter
Chapter 44 A/D Converter
This chapter provides an overview of the A/D converter, describes the register structure and functions, and
describes the operation of the A/D converter.
• 1. Overview of A/D Converter
• 2. Block Diagram of A/D Converter
• 3. Registers of A/D Converter
• 4. Operation of A/D Converter
1. Overview of A/D Converter
The A/D converter converts analog input voltage into digital values and provides the following features.
Features of A/D converter:
Conversion time: minimum 3 us per channel.
RC type successive approximation conversion with sample & hold circuit
10-bit or 8-bit resolution
Program section analog input from 32 channels
Single conversion mode: conversion of one selected channel
Scan conversion mode: continuous conversion of multiple channels, programmable for up to 32 channels
Single conversion mode: Convert the specified channel only once.
Continuous mode: Repeatedly convert the specified channels.
Stop mode: Convert one channel then temporarily halt until the next activation.
(Enables synchronization of the conversion start timing.)
A/D conversion can be followed by an A/D conversion interrupt request to CPU. This interrupt, an option that
is ideal for continuous processing can be used to start a DMA transfer of the results of A/D conversion to
memory.
Startup may be by software, external trigger (falling edge) or timer (rising edge).
■ Input impedance
Sampling circuit of A/D converter is expressed in Figure 1-1 Input Impedance
Figure 1-1 Input Impedance
Don•ft set Rext over maximum sampling time (Tsamp).
Rext = Tsamp/ (7*Cin) - Rin
Cin:max10.7pF
Rin
13.6kƒ¶(AVCC•†4.0V)
2.52kƒ¶(AVCC•†4.5V)
ADC
An alog S WANx
An alog
signal
source
Rext