M38203M4 Datasheet, PDF (95/344 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
2.1 I/O pins
Œ

Ž

Charge time
T

‘
’
Charge time
CMOS I/O
port A ^{“L” output}
“H” output
t2
“H” output
Input
Read port state
t2
Input
Read port state
CMOS I/O
port B ^{“L” output}
“H” output
Input
t1
“H” output Input
CMOS I/O
“H” output
port C
“L” output
Input
“H” output Input
Fig. 2.1.9 Timing diagram 1 where switch A is pressed
The discharging time (Ž, ) after completion of charge in Figure 2.1.9 is shown with the following
expression.
The discharging time (T) is obtained with T = CR.
qThe capacitance of the virtual capacitor (C) is:
Capacitance of microcomputer output transistors and input transistors ... Approx. 10 pF
Capacitance of package pin ............................................................................. Several pF
+ Capacitance of each key wiring ....................................................................... Several pF
(minimum) Approx. 10 pF
qIn the leak current standard at 5 V, the maximum value is 5 µA and the standard value is 0.05 µA.
Accordingly, the minimum resistance (R) is 1 MΩ and the standard resistance is 100 MΩ.
In the above condition, the discharging time (T) is obtained as follows:
T (minimum) = 10 pF ! 1 MΩ = 10 ! 10^-12 ! 1 ! 10⁶ = 10 ! 10^-6 (s)
T (standard) = 10 pF ! 100 MΩ = 10 ! 10^-12 ! 100 ! 10⁶ = 1 ! 10^-3 (s)
Accordingly, the discharging time (T) is 10 µs (minimum) to 1 ms (standard).
3820 GROUP USER’S MANUAL
2–9