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THEORY OF OPERATION
2-2. Editing and Printing
2-2-1. Editing
The CPU reads data sequentially from RAM and edits it in accordance with program instructions stored in EPROM. The
edited data undergoes parallel-to-serial conversion in the gate array, and is then output to the thermal head’s drive
controller.
2-2-2. Thermal head
The thermal head contains 640 heat elements. Printing is carried out by switching these elements ON or OFF as required.
Note that Line Mode supports 600-dot printing only. During Line Mode operation, therefore, the logic always sends OFF
data to elements 1 to 20 and 621 to 640.
The thermal head contains a dedicated drive controller. The controller consists of a shift register, a latch circuit, and a
driver circuit, as illustrated below. The drive controller receives serial data (SI) from the drive control board in sync with
the CLOCK signal. The controller latches the incoming data (LATCH), then outputs it to the heat elements in sync with
the trailing edge of the STROBE signals. A data value of LOW corresponds to a heat-element value of ON.
Fig. 2-5 Thermal-Head Drive Circuit
STROBE5
STROBE4
STROBE3
STROBE2
STROBE1
LATCH
SI
CLOCK
COM
Latch
Shift Register