Sunday, July 28

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Retrocomputing Journal

I've renamed the design from the A800 to the A750 because, duh, the processor is the H750.  If I follow up with the second design it will be the A1250 because the processor is the A1.

I've done a keyboard layout which can actually be made if this goes ahead.  Not cheap to order one, because it's all Cherry MX keyswitches, but hey.

https://ai.mee.nu/images/A750Keyboard.png?size=720x&q=95

I now know how to do AM, FM, and PWM via LFO on a software wavetable synthesizer; the FPGA I was thinking of using has dropped in price by 20%; and there's also a CPLD I can use for under A$3.

Advantage of the CPLD is that it's nonvolatile and starts up in half a millisecond.  Also, cheap.  The problem I had with the FPGA is that it's terribly inviting to use it for system control as well as the video controller, but then if you mess up while reconfiguring the video controller the whole system stops working.

So an $11 MCU for all the hard stuff, a $3 CPLD so that I won't need to suddenly add a random AND gate or latch somewhere, and a $7 FPGA to do video retiming and upscaling from the built-in LCD controller to proper 1080p - only if I can't get that to work in software, which I'll find out after the developer kit arrives.

As a nice touch they're all QFP-100 packages, which is not in any way necessary but is nice and clean.  CPU and custom chips all lined up neatly.  Hmm.  Need a QFP-100 DSP with 16-bit DACs...

That system control CPLD also means I can add a second VGA port running off a spare SPI output, in monochrome or possibly in character-cell colour.  So you can run one screen off that while you tinker with the settings for the LCD controller and FPGA on the other.  The added cost is just six resistors and the D-15 socket itself.

Update: Wait, how many SPI ports does the H750 have anyway?  I've assigned one to the "hard drive", one to console video, one to the TinkerPort, and one for internal expansion (which might be another TinkerPort).  Which is four gone before even thinking of anything else...  Six.  It has six.  Good.



Disclaimer: Flat out like a chicken dazzler.

Posted by: Pixy Misa at 02:22 AM | Comments (6) | Add Comment | Trackbacks (Suck)
Post contains 635 words, total size 6 kb.

1 " it will be the A1250 because the processor is the A1."
Brillant!
That's the kind of reasoning I employed when suggesting the next Xbox after the Xbox One be called the Xbox One Two.

Posted by: Rick C at Sunday, July 28 2019 04:20 AM (Iwkd4)

2 I'd go for a Sun type 4 layout, myself, except that I'd have to relearn the old backtick/tilde location. Amusingly, I just ran across someone who's done a USB conversion of a type 3.

-j

Posted by: J Greely at Sunday, July 28 2019 04:54 AM (ZlYZd)

3 Hey, my numbers are at least numbers!  And monotonic increasing!

As for the keyboard - I did have a different layout originally, but then looked up what could actually be produced one-off and changed it to this.  What I really want is an HP 9845 layout but I'm not sure that's entirely practical.

Posted by: Pixy Misa at Sunday, July 28 2019 05:39 AM (PiXy!)

4 I ordered an Ergodox Infinity a few months ago, but then some of the parts for it got hung up in customs in China.  Eventually it'll show up but I'm looking forward to trying out the multilayer thing.
"Xbox One" and "Xbox One Two" are monotonically increasing in *two* ways:  the next-next gen box could be called the XBox One Two Three.

Posted by: Rick C at Sunday, July 28 2019 07:57 AM (Iwkd4)

5 But there was also the 360.  razz

Posted by: Pixy Misa at Sunday, July 28 2019 04:21 PM (PiXy!)

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Posted by: Hannah Reeves at Monday, July 29 2019 08:36 PM (YvnWV)

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Apple pies are delicious. But never mind apple pies. What colour is a green orange?




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