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THEORY OF OPERATION
2-2-1. Editing
Data stored in the RAM is read out sequentially by the CPU and then edited according to a function code that has been
specified in advance.
This editing takes places until the CR or CR + LF code appears or the line buffer becomes full.
2-2-2. Print Head Driving Circuit
Edited print data is output to terminal Q in the gate array through the CPU data bus, as regulated by the issue timing of
a WR signal. However, as for pin 9 (HD9) of the print head, the data is output to the same terminal upon issue of the next
WR signal. When all the data is received for printing, an energized time control signal is output from port PO4 of the CPU.
This allows the print data to be output to HD-1 ~ 9 of the gate array. When the print data is HIGH, the transistor TR13
will be turned ON for 337 µS, energizing the print head solenoid to drive the print head.
Fig. 2-8 Print Head Driving Circuit
2-2-3. Print Head Temperature Detection Circuit
The print head temperature detection circuit protects against damage when the print head heats up abnormally. Fig. 2-9
shows this circuit.
The print head has a thermistor to show the temperature of the head solenoids. This thermistor is an element that converts
temperature into voltage. Its output voltage is input to an analog pin of the CPU. The CPU compares this input voltage
against its reference voltage Vref to find out the temperature of the head solenoids and carries out the following operations
depending on the temperature.
(1) T ≤ 115 ˚C
• Normal print operations
(2) 115 ˚C < T < 125 ˚C
• Interval printing; The print head stays for approximately 0.5 second whenever it finishes 1-line. When the
temperature falls bellow 115˚C, normal printing is resumed.
(3) 125 ˚C ≤ T
• The line being printed is completed, then printing stops. When the thermistor’s temperature falls below 125 ˚C,
interval printing is resumed.
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