Star Micronics TUP400 Series, Technical Manual

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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. Heat elements numbered 1 to 20 and 621 to 640 are always off.
(Off data is always being transmitted.)) The thermal head has a built-in 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 Resistor