SIC63616-(Rev. 1.0) NO. P153
3240-0412
R/f conversion sequence
An R/f conversion for the reference resistance starts by writing "1" to the RFRUNR register.
However, an initial value must be set to the measurement counter and the time base counter must be
cleared to "00000H" before starting the R/f conversion.
When R/f conversion is initiated by the RFRUNR register, oscillation by the reference resistance begins,
and the measurement counter starts counting up from the initial value by the oscillation clock. The time
base counter also starts counting down by the OSC1 clock.
If the measurement counter becomes "00000H" due to overflow, the oscillation is terminated. At the
same time an interrupt occurs and the RFRUNR register is set to "0", and the R/f converter circuit stops
operation completely.
The time base counter value should be saved into the RAM for R/f conversion of the sensor.
Figure 4.13.4.1 shows a timing chart for the reference oscillation.
Interrupt is generated
R/f converter clock
RFRUNR register
RFIN0/1
Time base counter clock
Time base counter
Measurement counter clock
(RFOUT output)
Measurement counter
n
*
n+1
n+2
FFFFFH
00000H
*
: Initial setting value (complement) for counting of reference resistance
00000H FFFFFH FFFFEH FFFFDH FFFFCH FFFFBH
x+3
x+2
x+1
x
Time base counter starts counting (count-down)
Starts measurement of reference resistance
Measurement counter starts counting
Fig. 4.13.4.1 Reference oscillation timing chart
An R/f conversion for the sensor starts by writing "1" to the RFRUNS register. When performing this
sensor oscillation after an reference oscillation has completed, it is not necessary to set initial values to
the counters. If converting the sensor resistance independently, the measurement counter must be set to
"00000H" and the time base counter must be set to the value measured at the time of a reference oscilla-
tion. When R/f conversion is initiated by the RFRUNS register, oscillation by the sensor begins, and the
measurement counter starts counting up from "00000H" by the oscillation clock. The time base counter
also starts counting up by the input clock. If the time base counter becomes "00000H", the oscillation
is terminated. At the same time an interrupt occurs and the RFRUNS register is set to "0", and the R/f
converter circuit stops operation completely.
Figure 4.13.4.2 shows a timing chart for the sensor oscillation.
Interrupt is generated
Time up
R/f converter clock
RFRUNS register
RFIN0/1
Time base counter clock
Time base counter
Measurement counter clock
(RFOUT output)
Measurement counter
00000H 00001H
00002H
n-1
n
*
*
: Number of counts during sensor oscillation
x
x+1
x+2
x+3
x+4
x+5
FFFFEH FFFFFH 00000H
Time base counter starts counting (count-up)
Starts measurement of sensor
Measurement counter starts counting
Fig. 4.13.4.2 Sensor oscillation timing chart
By the above operation, the sensor is oscillated for the same period of time as the reference resistance is
oscillated. Therefore, the difference in oscillation frequency can be measured from the values counted
by the measurement counter.