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CHAPTER 13 A/D CONVERTER
User
’
s Manual U14260EJ3V1UD
13.2 A/D Converter Configuration
The A/D converter consists of the following hardware.
Table 13-1. Registers of A/D Converter Used on Software
Item
Configuration
Registers
Successive approximation register (SAR)
A/D conversion result register 0 (ADCR0)
A/D converter mode register 0 (ADM0)
Analog input channel specification register 0 (ADS0)
(1) ANI0 to ANI7 pins
These are the analog input pins of the 8-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 0 (ADS0) can be used as input port pins.
Cautions 1. Use ANI0 to ANI7 input voltages within the specification range. If a voltage higher than or
equal to AV
REF
or lower than or equal to AV
SS
is applied (even if within the absolute maximum
rating range), the conversion value of that or equal to channel will be undefined and the
conversion values of other channels may also be affected.
2. Analog input (ANI0 to ANI7) pins are alternate-function pins that can also be used as input
port pins (P10 to P17). When A/D conversion is performed by selecting any one of ANI0
to ANI7, do not access port 1 during conversion, as this may cause a lower conversion
resolution.
3. When a digital pulse is applied to a pin adjacent to the pin in the process of A/D conversion,
A/D conversion values may not be obtained as expected due to coupling noise. Thus, do
not apply a pulse to a pin adjacent to the pin in the process of A/D conversion.
(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) Series resistor string
The series resistor string is connected between AV
REF
and AV
SS
, and generates a voltage to be compared with
the analog input signal.
Figure 13-2. Circuit Configuration Diagram of Series Resistor String
AV
REF
AV
SS
P-ch
Series resistor string
ADCS0