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 Post subject: Questions on SBC3
PostPosted: Mon Nov 28, 2016 5:01 pm 
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Location: Soddy-Daisy, TN USA
I have a few questions regarding the SBC3 computer. I would contact Daryl directly but I thought, perhaps, his response may help others.

http://sbc.rictor.org/info3.html

1) I don't have a deep understanding of the '816. But it seems to me that one would want to use 16 bit SRAM. Which is more expensive. Why wasn't 16 bit SRAM used? Please don't take this as criticism.

2) What would be a good, modern replacement for the CPLD in this design? There are so many to choose from and I don't think the exact same CPLD is available anymore as new stock.

3) Do you have any for sale?

4) The CPLD you used (or a modern equivalent)...do you think it could handle VGA output with fast enough SRAM? Or, would an FPGA be better for this? (or a much larger CPLD)?

Thanks for any response you can provide!

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 Post subject: Re: Questions on SBC3
PostPosted: Mon Nov 28, 2016 8:33 pm 
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Joined: Fri Aug 30, 2002 9:02 pm
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Location: Sacramento, CA
cbmeeks wrote:
I have a few questions regarding the SBC3 computer. I would contact Daryl directly but I thought, perhaps, his response may help others.

http://sbc.rictor.org/info3.html

1) I don't have a deep understanding of the '816. But it seems to me that one would want to use 16 bit SRAM. Which is more expensive. Why wasn't 16 bit SRAM used? Please don't take this as criticism.

Since the 65816 still uses an 8 bit external data bus, I didn't see the benefit of using 16 bit SRAM. (No offense taken)

2) What would be a good, modern replacement for the CPLD in this design? There are so many to choose from and I don't think the exact same CPLD is available anymore as new stock.

I have not researched it myself, but others here have mentioned this chip: ATF1508AS ->http://forum.6502.org/posting.php?mode=quote&f=10&p=38082

3) Do you have any for sale?

Sorry, I did not buy any extras.

4) The CPLD you used (or a modern equivalent)...do you think it could handle VGA output with fast enough SRAM? Or, would an FPGA be better for this? (or a much larger CPLD)?

There are may issues to consider here. What resolution of VGA? 320x200x8bit pixels used 64,000 bytes on the SBC-3. You could possibly reconfigure the XC95108 to support VGA timing with a 320x200x8 display. In order to generate a square pixel, you may need to double the vertical line data. Having a larger resolution will require more memory and more processor time to generate a frame. I think that trade-off needs close consideration. An FPGA would work for sure, but you may need to drop the 65816 to 3.3V or use buffers.

Thanks for any response you can provide!

I'm happy to help!

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 Post subject: Re: Questions on SBC3
PostPosted: Mon Nov 28, 2016 9:58 pm 
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cbmeeks wrote:
1) I don't have a deep understanding of the '816. But it seems to me that one would want to use 16 bit SRAM. Which is more expensive. Why wasn't 16 bit SRAM used? Please don't take this as criticism.

We discuss this in another post you made.

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