Sinclair ZX80 / ZX81 / Z88 Forums

You bluddy genius

Can't wait to see it in the flesh!

Just tried with the SG81_b.rom CLCKFREQ.P now takes 202 frames !

Andy

Andy Rea wrote:Yes !!!! I've done it... 20Mhz

Incredible! Unbelievable! I am lacking words (in english tounge) to express my absolute enthusiasm about what you achieved!
Does this have any chance to run on a Sinclair mainboard? If not, is someone going to design a motherboard for this?

I happen to have a 20mhz Z80 in my toolbox, as well as fast RAM. What are you using as a ROM?
I would love to buy a 40MHz ULA for running my Zeddy in 20 MHz You quote a price. When will it be ready?

Hi Paul, you could if your willing to make several modifications to the issue 1 board make it work, as for the ULA/other logic trickry prepare for soldering lots of wires...

To run at 20Mhz, the ROM is copied to RAM and then RAM occupies the 0-8K, in fact RAM can occupy all 64K, i have 128K with 8K pages, 16-48K always uses pages 2,3,4,5. 0-8K, 8-16K can be freely assigned any of the 16 pages, also when ram occupies 0-8K it is write protected, but you can still modify it if you really want to, just use the same page in a different memory space (you can have a single page appear in more than 1 memory space) and modify it there...

48-64K when M1 is active (video) then pages 2,3 are used, when M1 is not active you can assign any page.

ultimately i'd like to include a single AY PSG, and with the Expertise of The Mighty SirMorris A ZXpand-a-like SD slot (some difference may be un-avoidable, E.G memory mapping will no longer be controlled by the CONFIG command.)

I'd like to make a PCB, but that is something for the future.

Regards Andy

That's great!
Congrats,
Zsolt

Great work Andy!

Andy Rea wrote: ultimately i'd like to include a single AY PSG, and with the Expertise of The Mighty SirMorris A ZXpand-a-like SD slot

That would probably be a SPI interface and 1 (or better 2) /cardselect signals. That could also be used for MEFISDOS mmc cards

Siggi

You know what I would like to see?
A demo using a full power of 20Mhz ZX81. I think it would be a killer.

Andy Rea wrote:Hi Paul, you could if your willing to make several modifications to the issue 1 board make it work, as for the ULA/other logic trickry prepare for soldering lots of wires...

To run at 20Mhz, the ROM is copied to RAM and then RAM occupies the 0-8K, in fact RAM can occupy all 64K, i have 128K with 8K pages, 16-48K always uses pages 2,3,4,5. 0-8K, 8-16K can be freely assigned any of the 16 pages, also when ram occupies 0-8K it is write protected, but you can still modify it if you really want to, just use the same page in a different memory space (you can have a single page appear in more than 1 memory space) and modify it there...

48-64K when M1 is active (video) then pages 2,3 are used, when M1 is not active you can assign any page.

So I presume that a latch/register is used to control the bank switching. Is this part of the "40MHz" ULA or separate? If separate, which type are you using? And at what I/O address is it at?
I also presume that on power-up, a slower clock rate is active and the ROM is selected. Code then copies the ROM code to the RAM bank that can (after the copy completes) be switched in to the 0k to 8k of the memory map. Then presumably, a write is made to a memory address and the Zeddy then runs at 20MHz...

Well, I have an issue one PCB, a 20MHz Z80 and a fast SRAM chip (and lots of wire and solder...). So as Paul says, "You quote a price. When will it be ready?"

Mark

Andy Rea wrote:To run at 20Mhz, the ROM is copied to RAM and then RAM occupies the 0-8K

At the moment I am (still) experimenting with the STK16C88 Auto Store 32K RAM which is 25ns fast. It is in my (extended, zero insertion force) ROM Socket.
I want to do banking as well and when in 0-8K its write Protected, if it is also (same bank twice) in 8-16k you can modify it
But we should put this in a different thread. I just wanted to state there are fast options without copying the rom on every start... (and thus a mode skipping the copying would be fine )

CLCKFREQ.P new record (for me anyway)

frames taken: 194
speed 960.3%
freq 7.68Mhz

this is 20Mhz turbo mode, Wilf's Why wait circuit (coded in the CPLD), and the SG81_b rom as posted by Zsolt.

now then.... how do i get to 1000%...

Regards Andy