
APPLICATION
2.6 A-D converter
3822 GROUP USER’S MANUAL
2–142
sThe comparison voltage “Vref” is compared 8 times with the analog input voltage “VIN.” Each time a
comparison ends, the result is input to the A-D conversion register. With a change of the A-D con-
version register, the comparison voltage “Vref” changes, too.
Figure 2.6.1 shows changes in the A-D conversion register and comparison voltage during A-D con-
version.
Determination of the most significant bit (bit 7) of the A-D conversion register
Bit 7 is determined by the first comparison result.
The comparison voltage “Vref” is compared with the analog input voltage “VIN” and the result deter-
mines bit 7 as follows.
When Vref < VIN: bit 7 holds “1”
When Vref > VIN: bit 7 becomes “0”
Determination of bits 6 to 0 of the A-D conversion register
Bit 6 is determined by the second comparison result.
First, bit 6 of the A-D conversion register is set to “1.” Next, the comparison voltage “Vref” is
compared with the analog input voltage “VIN” and the result determines bit 6 as follows.
When Vref < VIN: bit 6 holds “1”
When Vref > VIN: bit 6 becomes “0”
Likewise, bits 5 to 0 are determined by the third to eighth comparison results.
With the above operations, the digital value (contents of the A-D conversion register) corresponding
to the analog input voltage “VIN” is determined by one bit at a time.
sUpon the completion of A-D conversion, bit 3 of the A-D control register is set to “1.”
An A-D conversion result can be obtained by reading out the A-D conversion register after bit 3 of the
A-D control register is set to “1.”
The A-D conversion result is held in the A-D conversion register until bit 3 of the A-D control register
is set to “1” again after the completion of the next A-D conversion.