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CHAPTER 12 8-BIT A/D CONVERTER (
µ
PD780344, 780344Y SUBSERIES)
User’s Manual U15798EJ2V0UD
12.2 8-Bit A/D Converter Configuration
The 8-bit A/D converter consists of the following hardware.
Table 12-1. 8-Bit A/D Converter Configuration
Item
Configuration
Analog input
8 channels (ANI0 to ANI7)
Registers
Successive approximation register (SAR)
A/D conversion result register 1 (ADCR1)
Control registers
A/D converter mode register 0 (ADM0)
Analog input channel specification register 0 (ADS0)
(1) Successive approximation register (SAR)
This register compares the analog input voltage value to the voltage tap (compare voltage) value applied from
the series resistor string, and holds the result from the most significant bit (MSB).
When up to the least significant bit (LSB) is held (end of A/D conversion), the SAR contents are transferred to
A/D conversion result register 1 (ADCR1).
(2) A/D conversion result register 1 (ADCR1)
ADCR1 is an 8-bit register that stores the A/D conversion result. Each time A/D conversion ends, the conversion
result is loaded from the successive approximation register.
ADCR1 is read by an 8-bit memory manipulation instruction.
RESET input sets ADCR1 to 00H.
ADCR1
Symbol
FF15H
Address After reset
00H
R/W
R
Caution When writing is performed to A/D converter mode register 0 (ADM0) and analog input channel
specification register 0 (ADS0), the contents of ADCR1 may become undefined. Read the
conversion result following conversion completion before writing to ADM0, ADS0. Using a
timing other than the above may cause an incorrect conversion result to be read.
(3) Sample & hold circuit
The sample & hold circuit samples the signal input to the analog input pin selected by the selector when A/D
converter is started. This circuit holds the sampled analog input voltage value during A/D conversion.
(4) Voltage comparator
The voltage comparator compares the sampled analog input voltage to the series resistor string output voltage.
(5) Series resistor string
The series resistor string is connected between AV
DD
and AV
SS
, and generates a voltage to be compared to the
analog input.
Содержание mPD780344 Series
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