Datasheet

CHAPTER 9 A/D CONVERTER (
μ
PD78F920x ONLY)
User’s Manual U18172EJ3V0UD
159
Figure 9-2 shows the block diagram of A/D converter.
Figure 9-2. Block Diagram of A/D Converter
V
DD
V
SS
INTAD
2
ADS1 ADS0
V
SS
ANI0/P20/TI000
TOH1
ANI1/P21/TI010/
TO00/INTP0
ANI2/X2/P22
ANI3/X1/P23
ADCS FR2 FR1 ADCEFR0
3
Sample & hold circuit
Voltage comparator
Controller
A/D conversion result register
(ADCR, ADCRH)
Analog input
channel specification
register (ADS)
A/D converter mode
register (ADM)
Internal bus
Successive
approximation
register (SAR)
Selector
D/A converter
Cautions 1. In
μ
PD78F920x, VSS functions alternately as the ground potential of the A/D converter. Be
sure to connect VSS to a stabilized GND (= 0 V).
2. In
μ
PD78F920x, VDD functions alternately as the A/D converter reference voltage input. When
using the A/D converter, stabilize V
DD at the supply voltage used (2.7 to 5.5 V).
9.2 Configuration of A/D Converter
The A/D converter consists of the following hardware.
(1) ANI0 to ANI3 pins
These are the analog input pins of the 4-channel A/D converter. They input analog signals to be converted into
digital signals. Pins other than the one selected as the analog input pin by the analog input channel specification
register (ADS) can be used as I/O port pins.
(2) Sample & hold circuit
The sample & hold circuit samples the input signal of the analog input pin selected by the selector when A/D
conversion is started, and holds the sampled analog input voltage value during A/D conversion.
(3) D/A converter
The D/A converter is connected between V
DD and VSS, and generates a voltage to be compared with the analog
input signal.
(4) Voltage comparator
The voltage comparator compares the sampled analog input voltage and the output voltage of the D/A converter.