LAPIS Semiconductor ML610421, User Manual, Page: 312 / 437

ML610Q421/ML610Q422/ML610421 User’s Manual
Chapter 24 RC Oscillation Type A/D Converter
24 – 8
24.3 Description of Operation
Counter A (RADCA0–2) is a 24-bit binary counter for counting the base clock (BSCLK), which is used as the standard
of time. Counter A can count up to 0FFFFFFH.
Counter B (RADCB0–2) is a 24-bit binary counter for counting the oscillator clock (RCCLK) of the RC oscillator
circuits. Counter B can count up to 0FFFFFFH.
Counters A and B are provided with overflow flags (OVFA and OVFB, respectively). Each overflow output results in
generation of an RC-ADC interrupt request signal (RADINT). Use the RADI bit of the RC-AC mode register
(RADMOD) to select whether to generate an overflow interrupt by an overflow on Counter A or Counter B: setting
RADI to “0” specifies Counter A overflow and setting it to “1” specifies Counter B overflow.
The RARUN bit of the RC-AD control register (RADCON) is used to start or stop RC-ADC conversion operation.
When RARUN is set to “0”, the oscillator circuits stop, so that counting will not be performed. When RARUN is set
to “1”, RC oscillation starts, when the RC oscillator clock (RCCLK) and the base clock (BSCLK) start counting
through Counter B and Counter A.
The RC oscillation section has a total of eight types of oscillation modes based on the two oscillator circuits of
RCOSC0 and RCOSC1, and mode selection is made by the RC-ADC mode register (RADMOD).
P30–34, P44–47, and P35 must be configured as their secondary function input or output when using 1) the RC
oscillator circuit RCOSC0, 2) the RC oscillator circuit RCOSC1, and 3) the RC monitor pin (RCM) that outputs RC
oscillation waveforms, respectively. For the configuration of the RC oscillator circuits, see Section 24.1.2,
“Configuration”; for the secondary functions of Port 3, see Chapter 20, “Port 3”; for the secondary functions of Port 4,
see Chapter 21, “Port 4”.
24.3.1 RC Oscillator Circuits
RC-ADC performs A/D conversion by converting the oscillation frequency ratio between a reference resistor (or
capacitor) and a resistive sensor (or capacitive sensor) such as a thermistor to digital data.
By making RC oscillation occur both on the reference side and on the sensor side with the reference capacitor the error
factor that the RS oscillator circuit itself is eliminated, thereby making it possible to perform the A/D conversion of the
characteristics of the sensor itself.
Also, by calculating the ratio between the oscillation frequency on the reference side and that on the sensor side and
then calculating the correlation between the calculated ratio and temperatures that the sensor characteristics have in
advance, a temperature can be obtained based on that calculated ratio.
Table 24-1 lists the eight types of oscillation modes, one of which is selected by the RC-ADC mode register
(RADMOD) OM3–0 bits.
Table 24-1 Oscillation Modes from Which Selection Is Made by OM3–0 Bits
Mode
No.
RADMOD RCOSC0 output pin RCOSC1 output pin Mode
OM3 OM2 OM1 OM0 RS0 RT0 RCT0 CS0 RS1 RT1 CS1
0 0 0 0 0 Z Z Z Z Z Z Z IN0 external clock input mode
1 0 0 0 1 1/0 Z Z 0/1 Z Z Z
RS0–CS0 oscillation
RCOSC0
oscillation mode
2 0 0 1 0 Z 1/0 Z 0/1 Z Z Z RT0–CS0 oscillation
3 0 0 1 1 Z Z 1/0 0/1 Z Z Z
RT
0-1
–CS0 oscillation
4 0 1 0 0 1/0 Z 0/1 Z Z Z Z
RS0–CT0 oscillation
5 0 1 0 1 Z Z Z Z 1/0 Z 0/1 RS1–CS1 oscillation
RCOSC1
oscillation mode
6 0 1 1 0 Z Z Z Z Z 1/0 0/1
RT1–CS1 oscillation
7 0 1 1 1 Z Z Z Z Z Z Z IN1 external clock input mode
8 1 * * * Z Z Z Z Z Z Z (Setting prohibited)
Note) * : Indicates “arbitrary.”
Z : Indicates high-impedance output.
1/0, 0/1 : Indicates active output.
(Setting prohibited)
: The oscillator clock is not supplied even by setting the RARUN bit to “1” or by
starting A/D conversion.