Star Micronics TSP400 technical manual Editing and Printing, Theory Of Operation

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.

COM

STROBE5

STROBE4

STROBE3

STROBE2

STROBE1

LATCH

Latch

SI

Shift Register

CLOCK

Fig. 2-5 Thermal-Head Drive Circuit

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