Brother P-touch 65, Service Manual

Page: 46 / 68

III - 10
3.2.7 Thermal Head Drive Circuit
Figure 3.2-10 shows the thermal head drive circuit.
The print head has an integrated heat generator (consisting of 64 heating elements
vertically aligned in 240 dpi) and a built-in driver IC.
Synchronizing with the clock on P02, the CPU outputs print data on P00 in the serial
form. Upon receipt of P01 signal issued by the CPU, the thermal head control circuit
latches the print data and drivers the heating elements of the thermal head according to
the signal issued from P03. Figure 3.2-11 illustrates a timing chart of the thermal head
drive.
Capacitor C10 works as a thermal head overheat protector. It cuts off the P03 signal to
shut down invalid drive current if the signal sticks to the low level due to any malfunctions
of the programs or the CPU.
Since thermal heads are very sensitive to heat and the head drive source is not
stabilized, the CPU determines the ON-time length of the P03 signal while monitoring the
head drive source voltage (refer to Subsection 3.2.8).
Figure 3.2-10 Thermal Head Drive Circuit