Brother PT 1800 - P-Touch 1800 Thermal Transfer Printer, Service Manual

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III - 8
Powering-off sequence (See Figure 3.2-6.)
1) Interrupted by IRQ0, the CPU starts the chattering elimination program module.
2) If pin 31 is Low for 10 ms, the CPU recognizes the On/Off key as being pressed
and then transfers the control to the sleep program module. If pin 31 is High, the
CPU interprets the input as a noise and keeps the main program module.
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 sleep program module.
[ 2 ] Power saving circuit
Figure 3.2-7 shows a circuit diagram of the power saving circuit. If you power off the
machine with the power On/Off key or you make no key entry for approx. 5 minutes, the
CPU turns P11 High to cut off the Vcc (which normally would feed power to the logic
circuits except the CPU). This way, the CPU enters the sleep mode where oscillation
stops so as to feed no clock to the CPU.
In the sleep mode, the +5BV feeds power only to the CPU.
To cancel the power saving mode (automatic powering-off mode) and resume the normal
operation mode, press the power On/Off key.
Figure 3.2-7 Power Saving Circuit