Brother DP-550CJ, Service Manual

Page: 44 / 194

THEORY
Electrical
SERVICE MANUAL
2-8
5.7. Clock Circuit
Four different clock circuits shown in Table 2.1 are incorporated in the main PCB.
Table 2.1 Clock Circuit
Clock Circuit Frequency Function
16MHz XT2 is the standard
clock for FDD control;
it inputs for #5 (pins
25, 26).
18MHz XT1 is the standard
clock for FDD control;
it inputs for #8 (pin
167).
20MHz XT3 is the standard
clock for printer control
and other several
timing; it inputs for #8
(pints 14, 15).
14.74MHz XT4 is the standard
clock for CPU core; it
inputs for #8 (pints 94,
95).
5.8. Buzzer Drive Circuit
The buzzer drive circuit is shown in Fig. 2.6. A 4 kHz pulse of 50% duty is output from
port BUZ (pin 25) of CBIC (#8) when buzzer operation is needed.
The piezoelectric element in BZ1 generates sound on reception of this pulse. The
output from port BUZ is Hi-Z when the buzzer is not in operation.
Fig. 2.6 Buzzer Drive Circuit