SIC63616-(Rev. 1.0) NO. P151
3240-0412
Two systems of CR oscillation circuits, channel 0 and channel 1, are built into the R/f converter and perform
CR oscillation with the external resistor and capacitor.
The counter that is used to obtain R/f converted values is shared with channel 0 and channel 1. Therefore,
operation for two channels is realized by switching the CR oscillation circuit that performs R/f conversion.
The channel to perform R/f conversion and the sensor type should be selected using the ERF0–ERF1
register in advance.
Table 4.13.3.2 Selecting channel and sensor type
ERF1
1
1
0
0
ERF0
1
0
1
0
Channel and sensor type
Ch.1 DC
Ch.1 AC
Ch.0 DC
I/O
DC: R/f conversion using a DC bias resistive sensor such as a thermistor
AC: R/f conversion using an AC bias resistive sensor such as a humidity sensor
(1) R/f conversion using a DC bias resistive sensor such as a thermistor
Channel 0 supports this conversion method only, and channel 1 is selected into this method by setting
ERFx to "11B". This method should be selected for R/f conversion using a normal resistive sensor (DC
bias), such as temperature measurement using a thermistor. At initial reset, channel 1 is set into this
conversion method.
Figure 4.13.3.1 shows the connection diagram of external elements.
R
SEN
R
REF
V
SS
C
RFC
R
SEN
R
REF
Open
C
RFC
SEN0
(P02)
REF0
(P01)
RFIN0
(P00)
Channel 0
V
SS
SEN1
HUD
REF1
RFIN1
Channel 1
R
SEN
:
R
REF
:
C
RFC
:
Resistive sensor (e.g. thermistor)
Reference resistor
Oscillating capacitor
Fig. 4.13.3.1 Connection diagram in case of R/f conversion
CR oscillation waveforms are shaped by the schmitt trigger and sent to the measurement counter. The
clock sent to the measurement counter is also output from the RFOUT terminal while the sensor is oscil-
lating. As a result, the oscillation frequency can be measured by an oscilloscope or other equipment.
Since this monitor has no effect on oscillation frequency, it can be used to adjust R/f conversion accu-
racy.
Oscillation waveforms and waveforms output from the RFOUT terminal are shown in Figure 4.13.3.2.
RFIN0/1 terminal
RFOUT output
(Measurement counter clock)
V
DD
V
SS
V
DD
V
SS
Fig. 4.13.3.2 Oscillation waveform