
CHAPTER 13 A/D CONVERTER
Preliminary User’s Manual U16541EJ1V0UM
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13.2 Configuration
The A/D converter includes the following hardware.
Table 13-1. Configuration of A/D Converter
Item
Configuration
Analog inputs
12 channels (ANI0 to ANI11 pins)
Registers
Successive approximation register (SAR)
A/D conversion result registers 0 to 11 (ADA0CR0 to ADA0CR11)
A/D conversion result registers 0H to 11H (ADCR0H to ADCR11H): Only higher 8 bits
can be read
Control registers
A/D converter mode registers 0, 1 (ADA0M0, ADA0M1)
A/D converter channel specification register 0 (ADA0S)
(1) Successive approximation register (SAR)
The SAR 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 held down to the least significant bit (LSB) (i.e. when A/D conversion
has been completed), the contents of the SAR register are transferred to the ADA0CRn register.
Remark
n = 0 to 11
(2) A/D conversion result register n (ADA0CRn), A/D conversion result register nH (ADA0CRnH)
The ADA0CRn register is a 16-bit register that stores the A/D conversion result. ADA0ARn consist of 12
registers and the A/D conversion result is stored in the 10 higher bits of the AD0CRn register corresponding to
analog input. (The lower 6 bits are fixed to 0.)
The ADA0CRn register is read-only, in 16-bit units.
Moreover, when using only the higher 8 bits of the A/D conversion result, the ADA0CRnH register is read-only,
in 8-bit units.
Caution
A write operation to the ADA0M0 and ADA0S registers may cause the contents of the
ADA0CRn register to become undefined. After the conversion, read the conversion result
before performing write to the ADA0M0 and ADA0S registers. Correct conversion results
may not be read if a sequence other than the above is used.
Remark
n = 0 to 11
(3) Power-fail compare threshold value register (ADA0PFT)
The ADA0PFT register sets a threshold value that is compared with the value of A/D conversion result register
nH (ADA0CRnH). The 8-bit data set to the ADA0PFT register is compared with the higher 8 bits (ADA0CRnH)
of the A/D conversion result register.
This register can be read or written in 8-bit units.
Reset input clears this register to 00H.