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Circuit Description

A prototype circuit to demonstrate the Graphics LCD simulation component. These dot-matrix liquid-crystal displays can be used to display black-and-white bitmap images (actually, rather black-and-green or black-and-red etc., depending on the LCD backlight color).

The simulation model is based on the instruction set of the KS0108 controller chip from Samsung, but most dot-matrix liquid-crystal display controllers use a similar instruction set and interface. The 8-bit data bus can also be used in a (slower) 4-bit mode to save wires.

The design shown here uses two cascaded TTL-series 74590 8-bit counters to address a ROM, whose output data directly drives the GraphicsLCD simulation component. The ROM stores both the initialization sequence data and the image data for the display. To avoid extra logic, only the lower 4-bits of each ROM data word are used for actual display data, while two bits control the counter reset, and one bit drives the display control inputs.

Press the "reset" pulse-switch to reset the counters and re-load the image into the display.