LAPIS Semiconductor ML610421, User Manual, Page: 324 / 437

ML610Q421/ML610Q422/ML610421 User’s Manual
Chapter 24 RC Oscillation Type A/D Converter
24 – 20
where t
RCCLK
(RS0) is the oscillator clock period by reference resistor RS0 and t
RCCLK
(RT0) the oscillator clock period
by thermistor RT0.
Since the oscillation period is expressed by “t
RCCLK
= k
RCCLK

R

C”, t
RCCLK
(RS0) and t
RCCLK
(RT0) are expressed by the
following expressions:
t
RCCLK
(RS0) = k
RCCLK

(CS0+CVR)

RS0
……
Expression E
t
RCCLK
(RT0) = k
RCCLK

(CS0+CVR)

RT0
When expression E is substituted for expression D, nA1 will be:
nA1 = nA0

RT0
RS0
Since “nA0” (“4B0H” in this example) and RS0 are constants whose values are fixed, “nA1” is a digital value
proportional to RT0. This very “nA1” corresponds to “nT0” in expression A.
That concludes the description of the A/D conversion method using a thermistor. “nA1” that has been obtained must
further be converted to a value such as a temperature indication value for thermometer by program according to the
temperature-to-resistance characteristics of the themistor.
24.3.4 Monitoring RC Oscillation
The RC oscillator clock (RCCLK) can be output using the secondary function of the P35 pin of Port 3. See Chapter
20, “Port 3,” for the details of the secondary function of P35.
Monitoring RC oscillation is useful for checking the characteristics of the RC oscillator circuit. That is, the
relationship between a sensor, such as a thermistor, and the oscillation frequency can be measured. For instance, the
coefficient for conversion from the above-described nA1 value to a temperature indication value can be obtained by
checking the relationship between the ambient temperature of a themistor-incorporated RC oscillator, the oscillation
frequency with thermistor RT0, and the oscillation frequency with reference resistor RS0.
Note:
•
P35 (RCM) is a monitor pin for oscillation clock. The channel 0(P34-P30) and channel 1(P47-P44) share the monitor
pin.
•
Please use P35 (RCM) for the evaluation purpose and disable the output while operating in an actual application to
minimize the noise.