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175
CHAPTER 11 A/D CONVERTER
User’s Manual U15017EJ2V0UD
Figure 11-1. Block Diagram of A/D Converter
(1) Successive approximation register (SAR)
This register compares the voltage value of the input analog signal with the value of the voltage tap (compare
voltage) from the series resistor string, and holds the result of the comparison, starting from the most significant
bit (MSB).
When the comparison result has been retained to this register up to the least significant bit (LSB) (i.e., when
the A/D conversion has been completed), the contents of this register are transferred to the A/D conversion
result register (ADCR).
(2) A/D conversion result register (ADCR)
This register holds the result of the A/D conversion. Each time the A/D conversion has been completed, the
conversion result is loaded to this register from the successive approximation register (SAR).
ADCR is read using an 8-bit memory manipulation instruction.
The value of this register is undefined when RESET signal is input.
(3) Sample & hold circuit
The sample & hold circuit samples the analog input signals sent from the input circuit one by one, and sends
them to the voltage comparator. It also holds the voltage value of the sampled analog input signal during
A/D conversion.
ANI0
ANI1
ANI2
ANI3
ANI4
ANI5
ANI6
ANI7
ANI8
ANI9
ANI10
ANI11
Sample & hold circuit
Voltage comparator
Successive
approximation register
(SAR)
Control
circuit
ADCS
Bit 7 of ADM
4
A/D conversion result
register (ADCR)
AV
DD
AV
SS
INTAD
A/D converter mode
register (ADM)
A/D converter input select
register (ADIS)
Internal bus
AV
SS
ADCS
0
FR2
FR1
FR0
0
0
0
ADIS3 ADIS2 ADIS1 ADIS0
S
T