
21 R/F CONVERTER (RFC)
S1C17705 TECHNICAL MANUAL
Seiko Epson Corporation
21-5
Functions for Measuring CR Oscillation Clock Frequency
21.4.3
CR Oscillation Clock (RFCLK) Monitoring Function
The CR oscillation clock (RFCLK) during converting can be output from the RFCLKO pin for monitoring. Use
this output to measure the oscillation frequency.
SSENA, SSENB, or SREF
RFINx pin
RFCLKO output
(Measurement counter clock)
VDD
VSS
4.3.1 CR Oscillation Clock (RFCLK) Waveform
Figure 21.
Continuous oscillation function
The CR oscillations by the sensor and reference element will automatically stop due to stop conditions. Setting
1 to CONEN/RFC_CTL register enables the continuous oscillation function and CR oscillation will continue
until stopped by software. Using this function with the CR oscillation monitoring function helps easily measure
the CR oscillation clock frequency.
RFC Counters
21.5
The R/F converter includes two kinds of counters: measurement counter (MC) counting the reference element and
sensor oscillation clocks, and time base counter (TC) counting the TCCLK clock.
Measurement counter (MC)
The measurement counter is a 24-bit presettable up counter. Counting the reference oscillation clock and the
sensor oscillation clock for the same duration in time using this counter minimizes errors caused by voltage,
and unevenness of IC quality, as well as external parts and on-board parasitic elements. The counter values
should be corrected via software after the reference and sensor oscillation are completed according to the sen-
sor characteristics to determine the value being currently detected by the sensor.
Time base counter (TC)
The time base counter is a 24-bit presettable up/down counter. The time base counter counts up by TCCLK
during reference oscillation to measure the reference oscillation time. During sensor oscillation, it counts down
from the reference oscillation time and stops the sensor oscillation when it reaches 0x0. This means that the
sensor oscillation time becomes equal to the reference oscillation time. The value counted during reference
oscillation should be saved in the memory. It can be reused at the subsequent sensor oscillations omitting refer-
ence oscillations.
Counter initial value
To obtain the difference between the reference oscillation and sensor oscillation clock count values from the
measurement counter simply, appropriate initial values must be set to the counters before starting reference os-
cillation and sensor oscillation.
Connecting the reference element and sensor with the same resistance/capacitance will result <Initial value>
= <Counter value at the end of sensor oscillation> (if no error introduced). Setting a small initial value to the
measurement counter improves measurement accuracy. However, the measurement counter may overflow dur-
ing sensor oscillation when the sensor value decreases below the reference element value (the measurement will
be cancelled). The initial value for the measurement counter should be determined taking the range of sensor
value into consideration.
The time base counter should be cleared to 0x0 before starting reference oscillation.