Epson S1C63656 Technical Manual page 128

CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (R/f Converter)
MC0–MC19: Measurement counter (FF92H–FF96H)
The measurement counter counts up according to the CR oscillation clock. It permits writing and reading
on a 4-bit basis.
The complement of the number of clocks to be counted by the oscillation of the reference resistance must
be entered in this counter prior to reference oscillation. When the counter reaches 00000H due to over-
flow, the oscillation of the reference resistance stops. When converting a sensor oscillation, 00000H must
be set in this register (it is unnecessary when it is done immediately after a reference oscillation has
completed). The sensor oscillation and measurement counter stop when the time base counter overflows.
Number of clocks counted by the sensor oscillation can be evaluated from the value indicated by the
counter when it stops. Calculate the target value by processing the above counted number according to
the program. Measurable range and the overflow of the counter must be taken into account when setting
an initial value to be entered prior to R/f conversion.
At initial reset, this counter is undefined.
TC0–TC19: Time base counter (FF97H–FF9BH)
Writing and reading is possible on a 4-bit basis by the time base counter that is used to adjust the CR
oscillation time between the reference resistance and the sensor.
The time base counter counts down during oscillation of the reference resistance and counts up to 00000H
during oscillation of the sensor.
00000H needs to be entered in the counter prior to a reference oscillation in order to adjust the CR
oscillating time (number of clocks) of both counts. The counter value after a reference oscillation has
completed should be read from this register and save it in the memory. The saved value should be set in
this counter before starting a sensor oscillation.
At initial reset, this counter is undefined.
RFCLK: Input clock selection (FF90H•D2)
Selects the clock input to the time base counter.
When "1" is written: OSC3
When "0" is written: OSC1
Reading: Valid
Select the count clock for the time base counter. When "1" is written to RFCLK, the OSC3 clock is selected.
When "0" is written, the OSC1 clock (Typ. 32 kHz) is selected. To select the OSC3 clock, the OSC3 oscilla-
tion frequency must be 2 MHz or less.
At initial reset, this register is set to "0".
RFSEL: Sensor selection for channel 1 (FF90H•D1)
Selects a sensor type to be used for channel 1.
When "1" is written: Resistive humidity sensor
When "0" is written: Resistive sensor
Reading: Valid
When "1" is written to RFSEL, a resistive humidity sensor is selected as the sensor for channel 1. When "0"
is written, a normal resistive sensor is selected.
At initial reset, this register is set to "0".
SENSEL: Channel selection register (FF90H•D0)
Selects the channel to be converted.
When "1" is written: Channel 1
When "0" is written: Channel 0
Reading: Valid
When "1" is written to SENSEL, channel 1 is selected for R/f conversion and when "0" is written, channel
0 is selected.
At initial reset, this register is set to "0".
118
EPSON
S1C63656 TECHNICAL MANUAL