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diy vga signal from ram

ok, here i go, perhaps i little clearer this time;

i have looked at vga timing specs and at max graphics mode res. (640*480*256), i think the data sourcing (from ram), and subsequent signal generation suitable for standard vga compliant monitor is possible with cheap of the shelf components. i don't want to go down the road of pic or fpga. i don't want to try to implement any hardware acceleration, just output contants of ram to monitor. not tv.

replies already received suggest it is an acheivable goal, and continuing research on the net has unearthed another similar and successful project.

it's just something i want to do for fun and i wonder if anybody has any relevant experience they wouldn't mind sharing.

re. the article by enoch hwang in circuit cellar, i don't suppose anyone could post a copy, i've paid my $1.50 online but the password popup didn't appear to function.

thanks for any info received. apologies to anyone who finds my presence a nuisance.

mike

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Reply to
mike
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How do you intend to fill the RAM?

Reply to
Ian Stirling

It's certainly do-able in discrete logic, and you will learn a lot in the process of doing it, but why bother learning what is an essentially obsolete skill... why not teach youself a more up-to-date method by doing it on a micro or FPGA ? It will probably take a similar amount of time, but at the end of it you will probably have a more useful (and marketable) knowledge base. Xilinx do a $99 eval board which, coincidentally, incldudes a VGA port for doing exactly this....

Reply to
Mike Harrison

May I suggest this: have two banks of RAM, one being read out by the display circuitry while the other is available to be written and read on a microprocessor bus. Have a bit on a port writable from the processor that when 0 has bank A switched to the processor bus and bank B displayed on video, and when set to 1 has bank B switched to the processor bus and bank A displayed on video. You generally don't want the processor to write to the active display RAM anyway. If you can do the memory updating within one frame refresh time (have a polled port available or do an interrupt at the vertical retrace so the processor can sync to it), and switch frames at the vertical retrace, and you can do "full animation."

But all this will soon be a lost art, as non-CRT displays will continue to fall in cost and change to a digital-only connection to computers.

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Reply to
Ben Bradley

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