CHAPTER 10 8-BIT A/D CONVERTER (
µµµµ
PD789426 AND 789446 SUBSERIES)
User’s Manual U15075EJ1V0UM00
184
Figure 10-1. Block Diagram of 8-Bit A/D Converter
Sample & hold circuit
Voltage comparator
Successive
approximation
register (SAR)
Controller
3
A/D conversion result
register 0 (ADCR0)
Tap selector
AV
SS
INTAD0
A/D converter mode
register 0 (ADM0)
Analog input channel
specification register 0 (ADS0)
Internal bus
AV
SS
P-ch
AV
DD
ANI4/P64
ANI5/P65
ANI0/P60
ANI1/P61
ANI2/P62
ANI3/P63
Selector
ADCS0 FR02
FR01
FR00
ADS02 ADS01 ADS00
(1)
Successive approximation register (SAR)
The SAR receives the result of comparing an analog input voltage and a voltage at a voltage tap
(comparison voltage), received from the series resistor string, starting from the most significant bit (MSB).
Upon receiving all the bits, down to the least significant bit (LSB), that is, upon the completion of A/D
conversion, the SAR sends its contents to A/D conversion result register 0 (ADCR0).
(2)
A/D conversion result register 0 (ADCR0)
ADCR0 holds the result of A/D conversion. Each time A/D conversion ends, the conversion result in the
successive approximation register is loaded into ADCR0, which is an 8-bit register.
ADCR0 can be read with an 8-bit memory manipulation instruction.
RESET input makes ADCR0 undefined.
(3)
Sample & hold circuit
The sample & hold circuit samples consecutive analog inputs from the input circuit, one by one, and sends
them to the voltage comparator. The sampled analog input voltage is held during A/D conversion.
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