ZX81 Homebrew Builders ..

[sirmorris]

We shall perhaps continue the discussion soon over a single malt?

[Moggy]

We shall perhaps continue the discussion soon over a single malt?

Whilst the discussion has just gone WHOOSE over my simple head the offer of a single malt sounds quite excellent good sir knight,and seeing as you have my address and having just dyked three quarters of a bottle of Glenlivet Founder's Reserve ,I look forward to your parcel arriving which I hope contains a bottle of the good stuff and not the usual electronic crap you knock up on your kitchen table when Lady Morris goes shopping.



Realising he has overstepped the mark a very tipsy Moggy retires to his basket for a lie down.

[Paul]

Coming back ON TOPIC, I remember very well when I first visited the UK alone in 1981 which not only showed me the ZX80 in a shop but also those homebrew kits from boots. Homebrewing was popular in 1981 in the UK. I brought some kits from boots home to germany that year....

[Moggy]

Coming back ON TOPIC, I remember very well when I first visited the UK alone in 1981 which not only showed me the ZX80 in a shop but also those homebrew kits from boots. Homebrewing was popular in 1981 in the UK. I brought some kits from boots home to germany that year....

Please tell me they were not the dreaded Tom Caxtons home brew kit.

http://www.the-home-brew-shop.co.uk/aca ... op-UK.html


Absolute drek in a can.

[Digital Harry]

er, how can you tell a 'fake' one, i bougĥt a fair load of 20mhz z80s from a seller in china, and would like to know if i've been diddled..theres another seller selling similar but even cheaper, print on chips seems to be different, white, the others were darker, grey/brown/orangey, maybe laser etched?

Most of the Cheapy Z84C0020PECs on ebay are 'Remarked' old NMOS/CMOS Z80s ...still work fine and most people probably won't notice... but these are not 20MHz type...


I've bought some from this supplier and they seem Genuine :

http://www.ebay.com/itm/1pcs-Z80-CPU-Mi ... SwT6pVqcat

I bought 10pcs direct for $19.00 ,( $1/90 each) arrived in about 10 working days and all seems fine..tested at 16MHz+. : email : leo@tk-ic.com

[1024MAK]

There is a way to Test whether they're NMOS or newer CMOS.. but I can't remember off-hand.

Err, two ways are described in the posts above in this thread

Mark

[Digital Harry]

Got to confess it sounds rather intriguing if somewhat ambitious though would be great to see it working. The video circuit is especially interesting using a TMS9918 as a seocnd VDP would allow Porting of MSX 1 and ColecoVision games !!

Hope you keep us posted with your progress and all the Best

Timex Sinclair100/1500+ Project


I’m currently looking at design and building my own Hombrew Timex 1500+ computer , a sort of ‘Timex Turbo R’. The specification is pretty loose at the moment as I’m still doing the feasibility part with parts availability and costings to make sure I don’t hit any problem later down the line.

The General Specification is below.


Power Supply , 9-12V DC input, giving 5V 1.5A regulated to board.
CPU (Z84C0020) switchable between 6,8,12,16, & 24MHz !
Z80 KIO (Z84C9008VSC) giving counter Timer, SIO & PIO
Fast SRAM & Fast EEPROM
EPM7512 CPLD (surface Mount) as Glue and Video Logic (NTSC 60Hz)
8255 as CF card interface
SPI interface possible option?
512K Silicon Disc
TMS9918A as second video chip , as this has an external video input pin.
Sound YM2149 (or AY-3-8910) + SN76489 as these are cheap and easily sourced.
Real time Calendar & Clock
RS232 serial ports to connect to second CPU option



The most difficult part will be the video circuit as I’m wanting to use a TMS9918A as a second VDP (Video Display Processor) , though the TMS9918A has provision for an external composite NTSC video signal which it then superimposes it’s video signal on top making this task easier.

The EPM7512 will give all original video modes and some extra ones. These will be fed into DACs (Digital to Analogue Converters) as the CPLD (EPM7512) have no on chip DACs. These RGB signals will be fed into a CXA1645 (or similar) encoder to give NTSC composite video at 60Hz synchronised with the TMS9918A video signal.

This will give the following modes

32x24 Text (8x8 bit pattern) original mode
64 x24 Text (8x8 bit pattern)
85 x 24 Text (6x8 bit pattern)
85 x 48 Tile (6x4 bit pattern) each tile 256 will have colors
256 x 192 Graphics Mode bitmapped 4 Colors per pixel 12K RAM
512 x 192 Graphics mode bitmapped as original mode 12K
560 x 192 Graphics mode bitmapped with 70 x 24 color grid 14.5K RAM
640 x 172 Graphics mode bitmapped with 64 x 22 color grid 15.5K RAM

Then the TMS9918A modes on a separate graphics plane (superimposed).


It’s all just on the drawing board at the moment, but if anyone has any constructive comments or is doing something similar it would be good to hear from you ?

Costings

Z84C0008PEC 8MHz Z80 CPU DIP40………………………..$2.0
Z84C9008VSC 8MHz Z80 KIO (CTC,SIO,PIO) PLCC……….$2.50
UM61512 15ns Fast SRAM DIP42…………………………….$2.0
27Cxx EPROM faster than 150ns…………………………….$1.0
EPM7512 10ns Altera MAXCPLD... ………………………….$10.0
Intel 82C55 PIO CF Card ……………………………………...$1.50
Intel 82C55 PIO PATA Hard Drive……………………………..$1.50
Intel 8251 SIO Extra Serial Port………………………………..$2.50
Intel 8291 GPIB …………………………………………………$5.0
NVSRAM 512Kx8bit………………………………………….$3.0
DS12C887 RTC clock…………………………………………..$1.50
TMS9918ANL VDP…………………………………………….$5.0
DACs Digital / analogue………………………………………..<$10.0
AT89C2051 MCU for PS/2 Keyboard…………………………...$1.0

Total cost for ICs < $50

Extras
RS232 to USB adaptor … to be costed
SPI interface …. still in pipeline

PCB (Double sided) Approximately $20 size yet to be determined
Power Jack $1.0
On/Off Switch $1.50
D -type connectors Various $13.0
DIL Sockets $5.0
9V or 12V , 1.5A Switch Mode PSU (Cheapy) $5.0

Total cost < $100.00

[Retro-Robert]

Video Circuit TIMEX Sinclair 1500+

Do you have any more details about the Video circuit , using a CPLD + DACs + NTSC encoder + TMS9918 ?? As if you could get this working it would be cool in many other homebrew microcomputers !

[mdave4953]

Video Circuit TIMEX Sinclair 1500+

Do you have any more details about the Video circuit , using a CPLD + DACs + NTSC encoder + TMS9918 ?? As if you could get this working it would be cool in many other homebrew microcomputers !

*********

The CPLD (Complex Programmable Logic Device), will generate digital RED,GREEN,BLUE output (RGB) probably 3 bits per color giving a palette of 512 Colors. These digital outputs will be fed into DACs (digital to analogue converters) to give analogue RGB then fed into a NTSC Encoder to give composite 50Hz NTSC video to be fed into the TMS9918ANL video in . The CPLD will be synchronised to the CPLD either via a RESET signal , shared with the TMS9918 or possibly by HYSNC,VSYNC, derived from the TMS9918 composite output signal, though this may be difficult. Synchronizing both videos will probably be quite hard ???

**********

[lezanderson]

If you are a homebrew builder looking for some FREE ICs... CPU,SRAM,EPROMs etc then look here :

http://www.mtxworld.dk/memorum/viewtopic.php?f=16&t=348

Dave's Website is here, were he can be emailed.

http://www.primrosebank.net/computers/mtx/mtx512.htm