10MHz, 12.5MHz and Beyond!

Using, learning, programming and modding the Gigatron and anything related.
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Joined: 09 Sep 2019, 08:19

Re: 10MHz, 12.5MHz and Beyond!

Post by PurpleGirl » 07 Oct 2019, 11:11

Potato Semiconductors only has a few of the logic chips used. I mention them since their chips run around the GHz range.


It seems they only have the OR gates and a couple of different buffer chips that are used by the Gigatron. It seems that they have none that are used by the accumulator or the ALU. These seem to be where the bottleneck is.
Last edited by PurpleGirl on 09 Oct 2019, 12:52, edited 1 time in total.

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Re: 10MHz, 12.5MHz and Beyond!

Post by at67 » 07 Oct 2019, 13:52

I've been playing with this ROM for the last couple of days and wow, Gigatron12.5MHz here I come.

P.S. I don't get the truncated screen shown on real hardware and in other emulators on my emulation, is this something you solved in the ROM since those pictures were posted?
ROMv3y_0.jpg (376.27 KiB) Viewed 1670 times

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Re: 10MHz, 12.5MHz and Beyond!

Post by marcelk » 07 Oct 2019, 15:58

That ROM v3y hasn't changed. The programmed refresh rate is for 31.25 kHz at 12.5 MHz. So at that speed, shrink the displayed pixels...

Last week I tested it again on my 15 MHz system after soldering the last color resistors (I had ran out of 820 Ohms). But then I found the game controller doesn't register anything anymore, and the keyboard adapter can't keep up either: it was spitting out multiple keystrokes for every key pressed.

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Re: 10MHz, 12.5MHz and Beyond!

Post by bmwtcu » 20 Oct 2019, 22:49

Hi Marcel, just so I understand... I know that Dave Jones worked on the 4-layer PCB, but is it possible to buy one from you? Thanks!

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Re: 10MHz, 12.5MHz and Beyond!

Post by marcelk » 21 Oct 2019, 16:56

Simply drop us an email. We still have a few.

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Re: 10MHz, 12.5MHz and Beyond!

Post by Sugarplum » 01 Oct 2020, 00:55

It might not help much, but you could try making a skip-carry adder. Just replace the upper nibble adder with 2 adders with the carry-in line on one tied to Vcc and the other carry-in tied to the ground. Use the carry-out from the low nibble to drive a multiplexer that controls which high-nibble adder goes on the bus. For no carries, the latency should be about the same. For carries, this should reduce the latency by about 10 ns or so.

Beyond the other mods such as a more compact board, using the fastest surface-mounted parts, etc., adding another pipeline stage might be the only feasible option. However, that might cause there to be 2 delay slots and would require trampolines to be rewritten.

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