Are you into electronics and homebrew computer ??

A place to discuss the ZX80's and ZX81's younger brother - the Sinclair ZX Spectrum
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lezanderson
Posts: 28
Joined: Tue May 17, 2016 12:03 pm

Are you into electronics and homebrew computer ??

Post by lezanderson » Sat Oct 21, 2017 10:19 am

This may ( or may-not ) be of interest to anyone into Electronics and building their own DIY homebrew Z80 : ZX Spectrum microcomputer ?

I've talked a Chinese supplier into making homebrew DIY IC kits ..

Homebrew ZX Spectrum kits are available :

https://www.ebay.com/itm/Zilog-Z80-512K ... 2748355244

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

Though it's best to shop around on the web and get an idea of prices , so you don't pay too much

** As the original ZX spectrum ULA only uses about 144 Macrocells an EPM7512 CPLD will most certainly be adequate to make an 'Enhanced' ZX ULA.

They will also make kits to order , if asked.... though best to have a price in your head and tell them your target price..

If you need more help just ask and I see if i can help.

lezanderson
Posts: 28
Joined: Tue May 17, 2016 12:03 pm

Re: Are you into electronics and homebrew computer ??

Post by lezanderson » Fri Nov 03, 2017 10:10 am

Designing a Homebrew ‘ZX Spectrum Plus’

Specification

A real Z80 CPU at the core of the system, 128K or 512K SRAM with 64K ROM. A large CPLD such as an Altera EPM7512 as substitute for an enhanced ULA, the EPM7512 works at 5V on I/O lines, internal at 3.3V so can be interfaced easily with legacy CPUs like the Z80. The CPLD would give digital output, these would need to be converted to analogue RF for composite TV, via a PAL/NTSC encoder CXA1645. Two sound chips, AY-3-8910 & SN76489. Intel 82C55 PIO for CF Card or IDE interface. A Real Time Clock, namely DS12887. PS/2 keyboard could be interfaced via a low cost MCU (89C2051 or similar). MAX705 IC supervisor for RESET. Optional functionality could include , Floppy disc interface, Maths Co-Processor, Serial Ports,Parallel Ports and Counter Timer, via a Z80 KIO.

The CPLD would generate Graphics video output, Memory decoding, I/O decoding, Keyboard interface etc. Altera software is free on the web and USB Blaster programmers only cost a few dollars on eBay.com

Z80 CPU (8Mhz or better)
128k or 512k SRAM
64K ROM
Large CPLD to act as ULA and glue logic
AY-3-8910 Sound Chip
SN76489 second sound Chip
8255 PIO to act as CF card ord IDE interface
DS12C887 RTC Clock timer
89C2051 or similar MCU to interface to PS/2 keyboard
MAX705 IC supervisor (RESET button)
Op-Amps for Analogue video
CXA1645 or similar PAL/NTSC Composite encoder
7805 Voltage regulator (1.5A @ 5V output)

Optional
Z84C90xxVEC Z80 KIO (CTC, SIO, PIO)
AM9511 Maths Pro-Processor
uPD765 FDC Chip
SED9420 Data Separator for FDC
Costing:

Z80 CPU (Genuine Z80)..……..………………………...…...$2.50
128k………………………..………………………….…..…..$1.0
512k SRAM…………..……………………………….…...….$5.0
64K ROM……………………...………………………..…….$1.0
EPM7512AETC144…………………………………….…….$18.0
AY-3-8910 Sound Chip…………………………………..…...$1.50
SN76489 second sound Chip…………………………..……...$0.50
8255 PIO to act as CF card ord IDE interface………….……...$1.0
DS12C887 RTC Clock timer……………………………….….$1.50
89C2051 or similar MCU to interface to PS/2 keyboard……...$0.50
Op-Amps for Analogue video………………………………….$2.50
CXA1645 or similar PAL/NTSC Composite encoder …..…...$1.50
MAX705 IC supervisor (RESET button)……………………..$0.25
7805 Voltage regulator (1.5A @ 5V output) ……….………...$0.25

Miscellaneous
Reset Button, ON/OFF switch, Power Jack, D-Type connectors etc
PCB (double sided) approx the same size as ZX spectrum +/+2 ?

Total cost for ICs $36.0
Miscellaneous $14.0
PCB (depending on size) $30

Total cost approx $80.0 -$100

Of-course this is the easy part.
Programming the CPLD, designing the PCB, fault finding , debugging software and all that these things entail, these are the hard parts !!!

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