Brother P-touch BB4, Service Manual

Page: 52 / 66

III - 9
3.2.7 Oscillation Circuit
Figure 3.2-10 shows the oscillation circuit.
This circuit contains two oscillators to generate 8.00 MHz frequency which acts as a CPU
basic clock and 32.768 kHz frequency for calendar clock.
Figure 3.2-10 Oscillation Circuit
3.2.8 Voltage Detection Circuit
Figure 3.2-11 shows the voltage detection circuit.
Figure 3.2-11 Voltage Detection Circuit
This circuit, which is composed of divider resistors R8 and R9, steps down the power
source V
BT
fed from dry cells and feeds the output to analog input port AN1 on the CPU.
According to the drive source voltage, the CPU determines the optimum head driver
power.
If the voltage drops below the following level:
in entry mode or
during printing
in clock mode
Then, the machine will:
approx. 5.86V approx. 5.35V Display the "BATTERY" message.
approx. 5.35V approx. 4.94V
Turn the LCD off. (The internal clock
remains on.)
approx. 2.90V
Turn itself off. (The internal clock and other
settings will be reset.)