16 R/F COnVeRTeR
S1C63003/004/008/016 TeChniCal Manual
Seiko epson Corporation
16-11
(Rev. 1.1)
MC[19:0]: Measurement counter (FF66h–FF62h)
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 overflow,
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 sen-
sor 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 over-
flow 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.
TC[19:0]: Time base counter (FF6Bh–FF67h)
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.
Precautions
16.8
• When an error interrupt occurs, reset the overflow flag (OVMC or OVTC) by writing "1." The same error interrupt
will occur again if the overflow flag is not reset.
• When setting the measurement counter or time base counter, always write 5 words of data continuously in order
from the lower address (FF62H
→
FF63H
→
FF64H
→
FF65H
→
FF66H, FF67H
→
FF68H
→
FF69H
→
FF6AH
→
FF6BH). Furthermore, an LD instruction should be used for writing data to the measurement counter and a
read-modify-write instruction (AND, OR, ADD, SUB, etc.) cannot be used. If data other than low-order 4 bits is
written, the counter cannot be set to the desired value.
• The reference and sensor oscillation frequency IC deviation of the R/F converter may increase due to variations in
resistances and capacitances, and board conditions. The 1.5 V low-voltage type is especially sensitive. Take this
into consideration and perform evaluations sufficiently when using the R/F converter.
For the IC deviation, see "Characteristics Curves (RFC reference/sensor oscillation frequency - resistance charac-
teristic)" in Chapter 19, "Electrical Characteristics."