Putting a ZX81 onto a CPLD

[Andy Rea]

interesting, i never heard about that special out instruction, i have a variety of Z80's here i might, if i can find time rig something up to test it out.

regards Andy

[PokeMon]

I think you should know this document, shouldn't you ?

http://www.z80.info/zip/z80-documented.pdf

[lezanderson]

The simplest and probably the cheapest design might be.

Z80 CPU (cheapy) $1.0
EPM7128SLC84 CPLD $2.0 each
64K SRAM (UM61512 DIP32) $1.0-$1.50 each
EPROM (8K,or 32K,or 64K) $1.0 each
SAA1099 Sound Chip ($1.50 each) or SN76489 Sound Chip ($.50 each)

low cost double sided PCB (that you design yourself) $15.0

So you should be able to make a low cost (cheap) ZX81 for about $28 ..£20 or so.. This is obviously the easy part.. the hard part is putting all the glue logic onto the CPLD, design and building a working prototype, putting it onto an economic PCB etc etc.. Easier said than done !

[lezanderson]

Information only (for those that are into building homebrew computer):

http://stores.ebay.com/P-A-Electro-Comp ... 8692137013

[Retro-Robert]

Information only (for those that are into building homebrew computer):

http://stores.ebay.com/P-A-Electro-Comp ... 8692137013

I had spotted these kits... the ZX Spectrum one likes quite interesting.. I have bought stuff from them in the past so they are OK, though I always tend to buy direct and get things cheaper by not paying ebay fees. But it is sometimes best to shop around as you can get some of the ICs very Cheap .. Z80s are normally only $1.10 each from various sources on ebay.com !

[lezanderson]

I was thinking of putting some ZX81 Kits on Ebay and selling them at Cost to Homebrew Builders... Things like :

Kit 1 (Cost about £8.0)

Z84C00xxPEC DIP40 Z80 CPU
UM61512 DIP28 64K SRAM
W27C512 DIP28 64K EPROM
EPM7128SLC84-15 CPLD PLCC84 (with socket)
8255 Intel PIO
SAA1099 Sound Chip
SN76489 Sound Chip
7805 Regulator

Kit 2 (Cost £12.50 )

Z84C00xxPEC DIP40 Z80 CPU
Z84C90xxVEC Z80 KIO (SIO/CTC etc) PLCC
UM61512 DIP28 64K SRAM
W27C512 DIP28 64K EPROM
EPM7128SLC84-15 CPLD PLCC84 (with socket)
DS12887 RTC DIP
AM9511 FPU Maths- co-Processor DIP
8255 Intel PIO
SAA1099 Sound Chip
SN76489 Sound Chip
7805 Regulator

Not sure whether they'd sell , but it is a good way to get people interested in building ZX81/ Z80 hardware ?

If anyone can think of a kit just let me know..

[mdave4953]

Has anyone managed to put the ZX81 ULA *or enhanced ULA) into VHDL code to put onto a CPLD ... I've seen ZX81s using GALs to do the function of the original ULA so I'm assuming it's been done ?

[gozzo]

ula using gals??? where, where??!!

[Paul]

That was Andy Rea a loooooong time ago.
Later he made a CPLD version of the ULA and he is willing to share his verilog...

[gozzo]

i know about the cpld module, i bought one is there info on a gal version around somewhere??