Power On/Off Circuit And Power Saving Circuit; Power On/Off Circuit; Power Saving Circuit - Brother P-touch PT-210E Service Manual

Electronics
3.2.4

Power ON/OFF Circuit and Power Saving Circuit

[1]

Power ON/OFF circuit

Fig. 3.2-5 shows a circuit diagram of the power ON/OFF key. The CPU processes the
ON/OFF key state in a sequence quite different from other keys although it is on the
keyboard.
If you press the ON/OFF key, the signal IRQ0 interrupts the CPU on P21. Then, the
CPU switches P21 to the input port and enters the process which eliminates the
chattering part in the signal IRQ0.
Powering-on sequence (See Fig. 3.2-6.)
1) Interrupted by IRQ0, the CPU starts the chattering elimination program
module.
2) If P21 is Low for 10 ms, the CPU recognizes the ON/OFF key as being
pressed and then transfers the control to the main program module. If P21 is
High, the CPU interprets the input as a noise and waits for the next IRQ0.
3) Even if releasing the ON/OFF key makes a chattering noise so as to generate
IRQ0, the CPU interprets the signal as a noise for 10 ms (between ƒ and „)
and then transfers the control to the main program module.
Fig. 3.2-5 Power ON/OFF Circuit
Fig. 3.2-6 Powering-on and-off Sequence
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