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ML610Q421/ML610Q422/ML610421 User’s Manual
Chapter 24 RC Oscillation Type A/D Converter
24 – 11
OM3 OM2 OM1 OM0 Mode of oscillation
0
1 0 1
Oscillates with the reference
resistor RS1 and CS1
0
1 1 0
Oscillates with the sensor RT1
and CS1
Figure 24-5 When RCOSC1 Is Used for Measurement with One Resistive Sensor
24.3.2 Counter A/Counter B Reference Modes
There are the following two modes of RC-ADC conversion operation:
•
Counter A reference mode (RADMOD RADI = “0”)
In this mode, a gate time is determined by Counter A and the base clock (BSCLK), which is used as the time
reference, then the RC oscillator clock (RCCLK) is counted by Counter B within the gate time to make the content of
Counter B an A/D conversion value.
The A/D conversion value is proportional to RC oscillation frequency.
•
Counter B reference mode (RADMOD RADI = “1”)
In this mode, a gate time is determined by Counter B and the RC oscillator clock (RCCLK), and the base clock
(BSCLK), which is used as the time reference, is counted by Counter A within the gate time to make the content of
Counter A an A/D conversion value.
The /D conversion value is inversely proportional to RC oscillation frequency.
(1) Operation in Counter A reference mode
Figure 24-6 shows the operation timing in Counter A reference mode.
Following is an example of operation procedure in Counter A reference mode:

Preset to Counter A (RADCA2–0) the value obtained by subtracting the count value “nA0” from the maximum
value + 1 (1000000H). The product of the count value “nA0” and the BSCLK clock period indicates the gate
time.

Preset “000000H” to Counter B (RADCB2–0).

Set the OM3–OM0 bits of RADMOD to desired oscillation mode (see Table 24-1).

Set the RADI bit of RADMOD to “0” to specify generating of an interrupt request signal by Counter A overflow.

Set the RARUN bit of RADCON to “1” to start A/D conversion.
CS1
RS1
RT1
IN1
CS1
RS1
RT1