20Mhz ZX81 clone...
Re: 20Mhz ZX81 clone...
Well the board is now populated, mostly everything is working, implemented wilf rigter Why wait, increasing speed a little more go the AY sorted with auto wait state insertion if running in turbo mode, so far my tests with the sound chip have been successful and i have not heard any playback faults. gone with the mic/ear on one stereo socket, and the AY sound on the other stereo socket. got an annoting buzz on the audio (not very loud but you can hear it when no sound from the ay is playing) i think it's probably cause by the switching noise on the main 5V rail, will try with a separate regulated supply tomorrow.
Andy
Andy
what's that Smell.... smells like fresh flux and solder fumes...
- 1024MAK
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Re: 20Mhz ZX81 clone...
The noise on the audio from the AY sound chip could also be ground line noise.
If possible, take the ground line for the output connector (and any components that connect between the audio and ground) from the ground pin of the AY sound chip.
Also use a filter circuit for the +5V supply to the AY sound chip. I would try a series 47R or 100R resistor followed by 100uF and 100nF decoupling capacitors (which should be as close as possible to the supply pins of the AY sound chip).
Try to route the audio (and audio ground) signals away from any fast switching digital circuits (including the traces/tracks or wires)
Mark
If possible, take the ground line for the output connector (and any components that connect between the audio and ground) from the ground pin of the AY sound chip.
Also use a filter circuit for the +5V supply to the AY sound chip. I would try a series 47R or 100R resistor followed by 100uF and 100nF decoupling capacitors (which should be as close as possible to the supply pins of the AY sound chip).
Try to route the audio (and audio ground) signals away from any fast switching digital circuits (including the traces/tracks or wires)
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: 20Mhz ZX81 clone...
Picture of Andy at the time of posting the above:by Andy Rea » Sun Sep 30, 2012 3:49 am
I think someone was in the zone..!
Re: 20Mhz ZX81 clone...
Well sometimes I like to work in the night, too.
At 2 am or 3 am you can concentrate, no email, no ringing and only shit in TV.
At 2 am or 3 am you can concentrate, no email, no ringing and only shit in TV.
Re: 20Mhz ZX81 clone...
seems like i got it working and then posted nothing more typical of me, no documentation or anything. anyway
it has 20Mhz Z80
128K static ram ( split into 8K pages )
the full 64K can be RAM
0-16K is fully pageable
16-48K is always pages 2,3,4,5
48-64K is fully pageable ( but during video pages 2,3 )
other feature include
turbo (20Mhz)
8-16K ram wrx/udg switchable
m1not switchable
ZxPand-a-like (very very alike Thanks SirMorris) possible to page zxpand rom (once loaded to ram by special boot program) in and out
erm think thats about it... oh runs Sponzy slightly faster than original 48K spectrum !
regards Andy
it has 20Mhz Z80
128K static ram ( split into 8K pages )
the full 64K can be RAM
0-16K is fully pageable
16-48K is always pages 2,3,4,5
48-64K is fully pageable ( but during video pages 2,3 )
other feature include
turbo (20Mhz)
8-16K ram wrx/udg switchable
m1not switchable
ZxPand-a-like (very very alike Thanks SirMorris) possible to page zxpand rom (once loaded to ram by special boot program) in and out
erm think thats about it... oh runs Sponzy slightly faster than original 48K spectrum !
regards Andy
what's that Smell.... smells like fresh flux and solder fumes...
- 1024MAK
- Posts: 5103
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: 20Mhz ZX81 clone...
Does it still exist?
If yes, pictures please
Mark
If yes, pictures please
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: 20Mhz ZX81 clone...
You bet it still exsists, it's my goto Zeddy it's not pretty, but hey it works.
Top left clock wise, Z80, 40Mhz osc, 128K ram, 8K eeprom, 2 x AY sound chips piggy backed, just to the right ( tiny chip ) audio op-amp, then PIC for ZxPand, jtag header and finally CPLD on separate breakout board
Spaghetti underside
side view
other side (reset switch)
zxpand LED above keyboard
Regards Andy
Top left clock wise, Z80, 40Mhz osc, 128K ram, 8K eeprom, 2 x AY sound chips piggy backed, just to the right ( tiny chip ) audio op-amp, then PIC for ZxPand, jtag header and finally CPLD on separate breakout board
Spaghetti underside
side view
other side (reset switch)
zxpand LED above keyboard
Regards Andy
what's that Smell.... smells like fresh flux and solder fumes...
Re: 20Mhz ZX81 clone...
What ever happened to this project - would love to see it available - even if made possible via the ZXMore....
Rich Mellor
RWAP Software
RWAP Adventures
SellMyRetro
Retro-Printer Module
Also Involved in:
Icephorm
RWAP Software
RWAP Adventures
SellMyRetro
Retro-Printer Module
Also Involved in:
Icephorm
Re: 20Mhz ZX81 clone...
There is a chance as I made some modifications to the second revision of ZXmore having two different clocks but this has to be tested first. If it is working, the new one will work with 8 MHz instead of just 6.5 MHz and option to be increased later. So never give up hope.
Re: 20Mhz ZX81 clone...
Hi fella's,
So..., anyhow, whats involved in making zeddy go at 20Meg.?, I can think of something straight away, the hsync and vsync will require a 12bit counting chain, but what about any(if any) rom timing constants go? Maybe a requirement to switch between clocks on the fly like from 40MHz to 6.5MHz and back again.
Cheers for now
Commie
So..., anyhow, whats involved in making zeddy go at 20Meg.?, I can think of something straight away, the hsync and vsync will require a 12bit counting chain, but what about any(if any) rom timing constants go? Maybe a requirement to switch between clocks on the fly like from 40MHz to 6.5MHz and back again.
Cheers for now
Commie