UPD784020 Datasheet, PDF (35/90 Pages) NEC – 16/8-BIT SINGLE-CHIP MICROCOMPUTER

mPD784020, 784021
8.6 A/D CONVERTER
An analog/digital (A/D) converter having 8 multiplexed analog inputs (ANI0-ANI7) is incorporated.
The successive approximation system is used for conversion. The result of conversion is held in the 8-bit A/D
conversion result register (ADCR). Thus, speedy high-precision conversion can be achieved. (The conversion time
is about 10 ms at fCLK = 12.5 MHz.)
A/D conversion can be started in any of the following modes:
• Hardware start : Conversion is started by means of trigger input (INTP5).
• Software start : Conversion is started by means of bit setting the A/D converter mode register (ADM).
After conversion has started, one of the following modes can be selected:
• Scan mode : Multiple analog inputs are selected sequentially to obtain conversion data from all pins.
• Select mode: A single analog input is selected at all times to enable conversion data to be obtained
continuously.
ADM is used to specify the above modes, as well as the termination of conversion.
When the result of conversion is transferred to ADCR, an interrupt request (INTAD) is generated. Using this feature,
the results of conversion can be continuously transferred to memory by the macro service.
Fig. 8-7 Block Diagram of A/D Converter
ANI0
ANI1
ANI2
ANI3
ANI4
ANI5
ANI6
ANI7
INTP5
Sample-and-hold circuit
Voltage comparator
Edge
detector
Conversion
trigger
Trigger enable
A/ D converter mode
register (ADM)
Successive conver-
sion register (SAR)
Control
circuit
INTAD
8
A/ D conversion
result register (ADCR)
Series resistor string
R/2
AVREF1
R
R/2
AVSS
8
8
Internal bus
35