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2. Circuit Operation
There are 9 driver ICs aligned horizontally on the thermal head
and each one of these ICs can drive 192 heat emitting registers.
This means that one line is at a density of 192×9=1728 dots=(8
dots/mm). / White/Black (white=0, black=1) data in one line
increments is synchronized at IC1 pin 166 (THCLK), and sent from
IC1 pin 163 (THDAT) to the shift register of the ICs. The shift
registers of the 9 ICs are connected in series, and upon the shift
of dot increment 1728, all the shift registers become filled with
data, and a latch pulse is emitted to each IC from IC1 pin 167
(THLAT).
With this latch pulse, all the contents of the shift registers are
latched to the latch registers. Thereafter, through the addition of
strobes from the IC1 pins (159, 160) only black dot locations (=1)
among latched data activates the driver, and the current passes to
heat the emitting body causing heat emission. / Here, the three
line strobes, STB1 to STB2, impress at intervals of 9.216 msec, as
required for one-line printout. / The sequence is shown on the
next page. [Moreover, for the strobe width, the thermistor value
inside the thermal head is detected according to IC1 pin 207. (See
BLOCK DIAGRAM
().) Depending on that value, the strobe width is
recorded in ROM (IC2). / Accordingly, the strobe width is
determined. / When the thermal head is not used, the IC1 (170,
THON) becomes low, Q8 turns OFF, Q13 turns OFF, and the +24 V
power supply for the thermal head driver is not impressed to
protect the IC.
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