
21 R/F CONVERTER (RFC)
S1C17705 TECHNICAL MANUAL
Seiko Epson Corporation
21-3
3.2 IOSC/OSC3 Division Ratio Selection
Table 21.
CLKDIV[1:0]
Division ratio
0x3
1/8
0x2
1/4
0x1
1/2
0x0
1/1
(Default: 0x0)
The time base counter uses the clock selected here for counting. Selecting a high-speed clock improves the
conversion accuracy. However the clock must be selected so that the time base counter will not overflow in the
reference oscillation phase.
Clock enable
The clock supply is enabled with CLKEN/RFC_CLK register. The CLKEN default setting is 0, which stops
the clock. Setting CLKEN to 1 feeds the clock generated as above to the RFC circuit. If no RFC operation is
required, stop the clock to reduce current consumption.
Operating Modes
21.4
The R/F converter features three oscillation modes that use the RFC internal oscillator circuit and a mode for mea-
suring an external input clock. Also it includes a CR oscillation clock (RFCLK) monitoring function and continu-
ous oscillation function for measuring the oscillation clock frequency. Each channel can be set to a different mode.
Oscillation Mode
21.4.1
In measurements using the RFC internal oscillator circuit, operate the oscillator with the reference element and then
the sensor for the same duration in time to count each oscillation frequency. The sensor value can be determined
from the difference between the two count values by software. The R/F converter supports DC bias resistive or
capacitive sensors and AC bias resistive sensors. The RFC internal oscillator circuit can operate in three oscillation
modes corresponding to the sensor to be used that is specified by SMODE[1:0]/RFC_CTL register.
4.1.1 Oscillation Mode Selection
Table 21.
SMODE[1:0]
Oscillation mode
0x3
Reserved
0x2
DC oscillation mode for measuring capacitive sensors
0x1
AC oscillation mode for measuring resistive sensors
0x0
DC oscillation mode for measuring resistive sensors
(Default: 0x0)
DC oscillation mode for measuring resistive sensors (SMODE[1:0] = 0x0, default)
This mode drives the oscillator with the reference resistor and resistive sensor by applying DC bias voltage.
Select this mode when a DC bias resistive sensor is connected. This mode enables two resistive sensors to be
connected to a channel. One reference resistor and one reference capacitor is also required.
SENBx
SENAx
REFx
RFINx
RREF
RSEN1
RSEN2
RREF: Reference resistor
RSEN1: Resistive sensor (DC bias)
RSEN2: Resistive sensor (DC bias)
CREF: Reference capacitor
Current passing direction
(DC driving)
CREF
4.1.1 Connection Example in DC Oscillation Mode for Measuring Resistive Sensors
Figure 21.
When one resistive sensor only is used, leave the unused pin open.