NEC mPD780852 Series, Предварительное руководство пользователя

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CHAPTER 12 A/D CONVERTER
Preliminary User’s Manual U14581EJ3V0UM00
12.2 A/D Converter Configuration
A/D converter consists of the following hardware.
Table 12-1. A/D Converter Configuration
Item Configuration
Analog input 5 channels (ANI0 to ANI4)
Register Successive approximation register (SAR)
A/D conversion result register (ADCR1)
Control register A/D converter mode register (ADM1)
Analog input channel specification register (ADS1)
Power-fail compare mode register (PFM)
Power-fail compare threshold value register (PFT)
(1) Successive approximation register (SAR)
This register compares the analog input voltage value to the voltage tap (compare voltage) value applied from
the series resistor string, and holds the result from the most significant bit (MSB).
When up to the least significant bit (LSB) is set (end of A/D conversion), the SAR contents are transferred to
the A/D conversion result register.
(2) A/D conversion result register (ADCR1)
This register holds the A/D conversion result. Each time A/D conversion ends, the conversion result is loaded
from the successive approximation register.
ADCR1 is read with an 8-bit memory manipulation instruction.
RESET input clears ADCR1 to 00H.
Caution When write operation is executed to A/D converter mode register (ADM1) and analog input
channel specification register (ADS1), the contents of ADCR1 are undefined. Read the
conversion result before write operation is executed to ADM1, ADS1. If a timing other than
the above is used, the correct conversion result may not be read.
(3) Sample & hold circuit
The sample & hold circuit samples each analog input sequentially applied from the input circuit, and sends it to
the voltage comparator. This circuit holds the sampled analog input voltage value during A/D conversion.
(4) Voltage comparator
The voltage comparator compares the analog input to the series resistor string output voltage.
(5) Series resistor string
The series resistor string is in AV
REF
to AV
SS
, and generates a voltage to be compared to the analog input.
(6) ANI0 to ANI4 pins
These are five analog input pins to input analog signals to undergo A/D conversion to the A/D converter. ANI0
to ANI4 are alternate-function pins that can also be used for digital input.
Caution Keep the input voltage of ANI0 to ANI4 within the rated range. If a voltage outside the rated
range is input, the conversion value of that channel is undefined, and the values of the other
channels may be also affected.