CHAPTER 11 A/D CONVERTER
User’s Manual U13850EJ4V0UM
346
11.2 Configuration
The A/D converter includes the following hardware.
Table 11-1. Configuration of A/D Converter
Item
Configuration
Analog input
12 channels (ANI0 to ANI11)
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
Control registers
A/D converter mode register 1 (ADM1)
A/D converter mode register 2 (ADM2)
Analog input channel specification register (ADS)
(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 result of the comparison starting from the most significant bit (MSB).
When the comparison result has settled down to the least significant bit (LSB) (i.e., when the A/D conversion has
been completed), 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 H (ADCRH)
Each time A/D conversion has been completed, the result of the conversion is loaded to this register from the
successive approximation register. The higher 10 bits of this register holds the result of the A/D conversion (the
lower 6 bits are fixed to 0). This register is read using a 16-bit memory manipulation instruction. RESET input
sets ADCR to 0000H.
When using only higher 8 bits of the result of the A/D conversion, ADCRH is read using an 8-bit memory
manipulation instruction.
RESET input sets ADCRH to 00H.
Caution A write operation to A/D converter mode register 1 (ADM1) and analog input channel
specification register (ADS) may cause the ADCR contents to be undefined. After the
conversion, read out the conversion result before the write operation to ADM1 and ADS is
performed. Correct conversion results may not be read if the timing is other than the above.
(3) 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 also holds the sampled analog input signal
voltage during A/D conversion.
(4) Voltage comparator
The voltage comparator compares the analog input signal with the output voltage of the series resistor string.
(5) Series resistor string
The series resistor string is connected between AV
REF
and AV
SS
and generates a voltage for comparison with the
analog input signal.
Содержание MPD703030A
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