r5f21368sdfp Renesas Electronics Corporation., r5f21368sdfp Datasheet - Page 646

• Manufacturer Part Number: r5f21368sdfp
• Description: Renesas Mcu R8c Family / R8c/3xt-a Series
• Manufacturer: Renesas Electronics Corporation.

Under development
R8C/36T-A Group
R01UH0240EJ0001 Rev.0.01
Apr 28, 2011
Figure 25.12
The capacitance of the touch electrode is measured by measuring the voltage at CHxA while gradually discharging
the electric charge stored in Cc. Measurement can be executed with the following steps:
Either CHxA0 or CHxA1 is selected for CHxA and Va0 or Va1 is selected for Va by setting registers TSCHSEL0 to
TSCHSEL2.
(1) Charge Cc by connecting the CHxC pin to the voltage supply (VCC).
(2) After charging Cc fully, discharge Cc by connecting pins CHxA and CHxB to the ground level (VSS).
(3) After discharging Cc for a short period of time, keep pins CHxA, CHxB, and CHxC at high-impedance (Hi-
(4) Repeat steps (2) and (3).
(5) Set an input level for the CHxA pin using the VLT0 register (input threshold value control register 0).
(6) The count value is comprised of the primary counter value of data 1 and data 2.
As the finger comes closer to the touch electrode, a change of
following formula (B).
Z), and measure the voltage at the CHxA pin. At this point, as shown in Figure 25.11, when the voltage
measured at the CHxA pin is Va, and the voltage measured at the CHxC pin is Vc, Va at the time of voltage
measurement is expressed by the following formula (A).
The Time-dependent Variation of Va and Vc is shown in Figure 25.12.
Count the number of discharges before Va falls below the input threshold value. Continue counting until the
secondary counter reaches 0.
Preliminary document
Specifications in this document are tentative and subject to change.
Time-dependent Variation of Va and Vc
Voltage
Va (=
Va =
Va =
Charge Cc
Vc
Cr + Cx
Cr + Cx +
Cr + Cx
Cr
Cr
Measure Va at high-impedance
Vc)
Cr
Vc .............formula (A)
Repeat discharge and
Cx
high-impedance
Vc .................formula (B)
Cx is generated and Va is expressed by the
Time
25. Sensor Control Unit
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