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A parallel port and a demonstration of the Z80 computer

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benryves

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The last piece of hardware to add to the computer was a parallel port. These have eight data lines and nine assorted control and status lines. My last two 8-bit I/O expanders provide sixteen of these seventeen lines, and the final one was provided by the DS1307 real-time clock chip which happily has a spare pin on it that can be used as an output.

Parallel port I/O expanders Parallel port connector

This parallel port can be used to print from the computer. Some software has printing capabilities built in (such as the text editor VEDIT Plus), but by pressing Ctrl+P in CP/M any text sent to the display will be simultaneously sent to the printer.

I also needed to mount the LCD inside the case. I bought a plastic strip to try to make a nice frame for it, but couldn't cut it accurately enough by hand so have had to make do with merely sticking the LCD behind a rectangular hole cut in the aluminium. It's not the neatest arrangement and doesn't protect the LCD from scratches but is better than nothing.

To demonstrate the computer's hardware and software, I recorded a video:

">Demonstration video thumbnail
Watch video on YouTube

I'm not desperately happy with the way it came out; I really need to find a better microphone and the angle of the sun and variable weather when I made the video threw the white balance off. On the plus side, I did find out how to capture crisp black and white video with my TV capture card; I connected the composite video output from the computer to the luma pins on the S-video input on the capture card, then dropped the saturation to zero in VirtualDub. For some reason this produces great quality video, in comparison to the composite input which produces a fuzzy mess ? there shouldn't really be any difference with a black and white signal (regular television sets don't have any problems).
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Ah fantastic, you made a *proper* computer with real software to run on it. I seems to work really well from your video. I'm really very impressed with the whole thing. And sound now too!

I like the way you used three different kinds of microprocessor / controller in it :)

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all this is wonderful, and made me start my own project (or, to be precise, learning electronics to be able to start my own project), but I wanted to point out how incredibly professional the video looks. Ben, you should consider career in lecturing :D

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