The Custom TRS-80 model 1 Hi res option

Posted on Feb 4, 2014

The following project can either stand alone as a plug-in peripheral, or be integrated as part of the TRS-80 keyboard unit. In either case, the specifications are: The hardware involved in this project, including power supply and miscellaneous hardware, will be under $100 (probably closer to $70 by the time you read this), yet will compete easily with any

The Custom TRS-80 model 1 Hi res option
Click here to download the full size of the above Circuit.

high-resolution add-on for the TRS-80. On the negative side, this project will invoive a great deal of wire wrapping or soldering, and will eat up one chunk of 16K memory address space when it is used. It will not actually compete with or replace the top memory block in the expansion box (there is no electronic conflict) but will be addressed from COOO to FFFF. Alternatively, it may be addressed from 8000 to BFFF. In either case, you do not need the expansion box to run this memory. pixels by 3 pixels (a pixel is a picture element`) for the familiar coarse graphics mode accessed with SET and RESET. If you turn the contrast fully down and reduce the brightness of the screen, the individual dots which make up the graphic and alphanumeric characters can be seen with a sharp eye; a magnifying glass will make the dots very clear. In order to produce a complete screen line of letters, the locations in video memory are handed to a circuit which actually accesses them twelve times - once for each pass the electron beam makes horizontally. At each pass, a row of dots corresponding to part of the whole line of letters is shifted out to the video beam. Each dot (or undot`) then turns the hearn on or off for the tiny fraction of a second it takes to sweep across 1/384th of the screen. The point is clear: an electronic event takes place for every dot on every line of the screen. This means that it is possible to create an individual,...

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