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Parrot!

A project log for Novasaur Retrocomputer

Retrocomputer with serial and video built from only 1978-era TTL logic

Alastair HewittAlastair Hewitt 12/08/2019 at 05:041 Comment

One significant milestone in any home brew VGA project is to generate a parrot image... so here it is!

This is in the lo-res video mode (160x120) using the 3:3:2 video DAC. To do some baseline testing the board generating this does not have any decoupling capacitors and it looks pretty terrible. The video is being oversampled by a factor of 5 and a lot of the supply noise shows up in the image (the white area below should be the same color).

Hopefully this will be greatly improved with the Rev 2 board, which is where most of the time over the last 2 weeks has been spent. Also worth noting is how this image is generated. The image is stored in the ROM, but the Harvard Architecture prevents data from being read from the ROM. The image is actually the product of several ALU functions, each one acting as a lookup table to return parts of the bitmap image.

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Dave's Dev Lab wrote 12/08/2019 at 18:43 point

awesome!

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