LAPIS Semiconductor ML610421, User Manual, Page: 321 / 437

ML610Q421/ML610Q422/ML610421 User’s Manual
Chapter 24 RC Oscillation Type A/D Converter
24 – 17
Figure 24-14 shows, as an example of method, a timing diagram of one cycle of conversion from analog value RT0 to a
digital value, that is, A/D conversion.
Basically, one A/D conversion cycle must consist of two steps, as shown in Figure 24-14. The reason for requiring
two steps is that the reference resistor and the thermistor must first be oscillated separately and then the ratio between
the oscillation frequencies of them is used, as described above.
In the example below, operation for these two steps is performed using the following combination:
•
First step = RC oscillation with RS0 in Counter A reference mode
•
Second step = RC oscillation with RT0 in Counter B reference mode
Besides this, there would be several possible A/D conversion methods.
In the above method, the operation time (gate time) for the second step fluctuates depending on the value of thermistor
RT0. To avoid the fluctuation of the operation time, using a method that uses the following combination is
recommended:
•
First step = RC oscillation with RS0 in Counter B reference mode
•
Second step = RC oscillation with RT0 in Counter A reference mode