DEMOKIT-LG2 Renesas Electronics America, DEMOKIT-LG2 Datasheet - Page 21

• Manufacturer Part Number: DEMOKIT-LG2
• Description: KIT DEMO 78K0 LG2 UPD78F0397
• Manufacturer: Renesas Electronics America

Specifications of DEMOKIT-LG2

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

DemoKit-LG2 User’s Manual
The following equation, which approximates the characteristic curve, calculates temperature at the
sensor according to the change in the sensor’s resistance:
The temperature is measured using the dual-slope method in which a resistor value can be converted
into a digital countervalue. To do this, the charging time of capacitor C
bit timer/event counter 00 of the MCU. The first charging slope will use a reference resistor (R
and the second charging slope a variable resistor (R
comparing the two measured times and the known reference resistor R
calculated.
All of the 78K0/LX2 MCUs have bit-settable I/O ports and Schmitt-trigger inputs such as the TI000
timer input port. The DemoKit-LG2 uses the P0 bit-settable port as a bidirectional port.
At first, the complete port P0 is cleared and set to output mode. In this case, the C
discharged via P00/TI000 and prepared for the first measurement. The R
the current during the discharging of the capacitor. Then port P02 is set to 1 and output. At this point,
the 16-bit timer/event counter 00 is started. The rest of the port P0 is set to input (high impedance). So
the capacitor will be charged via the R
level of the Schmitt-trigger input P00/TI000, the actual timer value is automatically captured and an
T =
T =
25 +
25 +
with:
with:
Figure 8. Typical Dependence of Sensor Resistance
α² - 4 x β + 4 x β x k
α² - 4 x β + 4 x β x k
α = 7,88 x 10 x K
α = 7,88 x 10 x K
α = 7,88 x 10 x K
β = 1,937 x 10 x K
β = 1,937 x 10 x K
β = 1,937 x 10 x K
k
k
k
T
T
T
6
=
=
=
reference resistor. When the capacitor has reached the threshold
R
R
R
R
R
R
25
25
25
T
T
T
2 x β
2 x β
-3
-3
-3
VAR
-5
-5
-5
= R
-1
-1
-1
T
T
-2
-2
-2
5
+ R
- α
- α
T
), which should be determined. By
REF,
18
° C
° C
7
will be measured with the 16-
resistor is only used to limit
the variable resistor can be
18
capacitor is
REF
= R
15
6
)