
CHAPTER 11 A/D CONVERTER
User’s Manual U15905EJ2V1UD
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11.2 Configuration
The A/D converter consists of the following hardware.
Table 11-1. Configuration of A/D Converter
Item
Configuration
Analog input
12 channels (ANI0 to ANI11): V850ES/SA2
16 channels (ANI0 to ANI15): V850ES/SA3
Registers
Successive approximation register (SAR)
A/D conversion result register (ADCR)
A/D conversion result register H (ADCRH): Only higher 8 bits can be read
Power fail comparison threshold register (PFT)
Control registers
A/D converter mode register (ADM)
Analog input channel specification register (ADS)
Power fail comparison mode register (PFM)
(1) Successive approximation register (SAR)
This register compares the voltage value of the analog input signal with the voltage tap (compare voltage)
value from the series resistor string, and holds the comparison result starting from the most significant bit
(MSB).
When the comparison result has been saved down to the least significant bit (LSB) (A/D conversion
completion), the contents of the SAR are transferred to the A/D conversion result register.
(2) A/D conversion result register (ADCR), A/D conversion result register (ADCRH)
Each time A/D conversion has been completed, the result of the conversion is loaded to this register from the
successive approximation register, and the higher 10 bits of this register hold the result of the A/D conversion
(the lower 6 bits are fixed to 0).
The ADCR register is read-only, in 16-bit units. ADCR is undefined after reset.
When using only the higher 8 bits of the A/D conversion result, the ADCRH register is read-only, in 8-bit units.
Caution
When data is written to the A/D converter mode register (ADM) or analog input channel
specification register (ADS), the contents of the ADCR register may become undefined. Read
the conversion result after completion of conversion and before writing data to the ADM and
ADS registers. Otherwise, the correct conversion result may not be read.
(3) Power fail comparison threshold register (PFT)
This register sets the threshold when comparing with the A/D conversion result register.
The 8-bit data set in the PFT register and the higher 8 bits (ADCRH) of the A/D conversion result register are
compared.
The PFT register can be read or written in 8-bit units.
This register is cleared to 00H after reset.
(4) Sample & hold circuit
The sample & hold circuit samples each of the analog input signals sequentially sent from the input circuit and
sends the sampled data to the voltage comparator. This circuit holds the sampled analog input voltage during
A/D conversion.