http://forum.zbestshop.com//blog.php zBestshop Community en Sat, 22 Nov 2008 03:04:40 GMT vBulletin 60 http://forum.zbestshop.com/images/misc/rss.jpg http://forum.zbestshop.com//blog.php http://forum.zbestshop.com//blog.php?b=2 Mon, 07 Apr 2008 01:02:21 GMT How to build your own ZX80/ZX81! This page details the construction of your own ZX80. Follow this link to build an NMI generator which, when used... How to build your own ZX80/ZX81!
This page details the construction of your own ZX80. Follow this link to build an NMI generator which, when used with the ZX80 circuit detailed below and the ZX81 ROM, will produce a FULLY FUNCTIONING ZX81 USING OFF-THE-SHELF COMPONENTS!
(last updated 15th January 1999 )

• Introduction
• Construction
• Parts List
• Circuit Diagram
• ROM images
• Keyboard overlay
• Pictures of the finished ZX80
• Screen shots
• Software
• Pics of the original ZX80 kit
• Links to other sites of interest

Introduction

For many years now I have been working with the latest technology using high-powered computers. However, nothing nowadays can replace the time when the first home microcomputers hit the streets. I am a keen collector of the home computer era. Follow this link to see my current collection. In those days you HAD to make your programs fit the hardware and memory available. This added to the enjoyment of programming to see something you had written to fit in a few K spring to life. The later ZX81 is very similar to the ZX80 except a lot of the ICs in the 80 has been merged into one chip. As a result, you can learn a lot about the workings of the ZX81 by referring to the ZX80 circuit. I have several computers from the start of the 80's but have always liked the Sinclair ZX80 for the following reasons:

1. It was so tacky :)
2. It did not have a single dedicated IC in sight.

It is because of the second reason this page has come into existence. Here I show you how to build your own piece of history. ALL parts for the ZX80 are available from most of the larger electronic companies.
I must point out this is not a job for the absolute beginner. You will need to blow your own EPROM image and it will probably be a distinct advantage to have access to an oscilloscope in case it doesn't work. I can assure you the circuit supplied here DOES work without any modifications.
I have, however made the following modifications for my own version:

1. I originally used a 6264 SRAM to make the base memory 8K instead of 1K. I have since replaced this with a 62256 (a 32K x 8 chip) to bring the memory up to the "full 16K" (the unused address line is tied to a power line).
2. My TV has a video input socket so I did not use the video modulator (to save a few quid as I didn't have one in my spares box). I have since found one and now use the UHF output into a TV.
3. I could not get the ceramic resonator. Instead I used a crystal and used a load capacitance of 47pF.

To Be continued...

]]> Mikey http://forum.zbestshop.com//blog.php?b=2 http://forum.zbestshop.com//blog.php?b=1 Mon, 07 Apr 2008 00:42:15 GMT Image: http://forum.zbestshop.com/images/attach/image001.gif The ZX Spectrum is a small personal computer on the market in the United Kingdom in...

The ZX Spectrum is a small personal computer on the market in the United Kingdom in 1982. Based on the processor Zilog Z80 running at 3.5 MHz, the Spectrum was sold with either 16 or 48 kilobytes of memory (an extension was also available to increase from 16 to 48 kilobytes). Sold for 125 pound sterling (GBP) for the model 16 Kio and 175 GBP for the model 48 Kio, the Spectrum was the first personal computer the general public in Britain, similar in importance to the Commodore 64 in the United States (who was also Spectrum of a rival in Europe).



Fig 1

A slightly modified version of the Spectrum, in a silver body with hard plastic keys, was sold in the United States by Timex as the TS2068. He had an extension ROM 8 Kio additional cartridges for a port, two ports for joysticks and a microprocessor audio AY-3-8912; BASIC commands and additional order this material (STICK, SOUND). In the following models are the ZX Spectrum +, with an improved keyboard, and the ZX Spectrum 128, with better sound and 128 Kio RAM. After the purchase by Amstrad Sinclair Research in 1986, two additional versions were created: the ZX Spectrum +2 with a tape recorder included in the machine, and the ZX Spectrum +3 with a floppy 3 inches included.

A number of major game developers today began their careers on the ZX Spectrum, as Ultimate Play The game (today Rare, Inc.), Peter Molyneux (ex-Bullfrog Games), and Shiny Entertainment. Several clones were produced, particularly in Eastern Europe (Elwro, HC85), and South America. Some are still in production, such as the Sprinter Didaktik and Peters Ltd Plus. The video output was on a television with a color display. A keyboard with rubber above the membrane (similar to a calculator) inscription recalling keywords in the BASIC. Thus, in programming mode, pressing the 'G', for example, inserts the command BASIC GOTO. The programs were recorded on a tape recorder classic. Particularly in light of slow current technologies, it was not uncommon to load a program for 20 minutes before you can use, which prompted the manufacturer to develop its own system backup. The video display of Spectrum, although rudimentary compared to current standards, was perfect at the time for viewing on television and laptops has not been a hindrance to the development of video games. The text mode is 32 columns on 23 lines with a choice of eight colors in a normal mode is either brilliant, giving sixteen shades.

The graphic resolution is 256 ? 192 with the same limitations of colors. The Spectrum has an interesting approach to color management; Attributes colors are in a grid of 32 by 24, separate data graphics and text, with a limitation to only two colors per cell. This led to what was called color attribute clash or clash (collision of colors or attributes) that caused strange effects in the arcade-style games. Regarding sound, a simple beeper managed more or less to emit sounds rudimentary. For information, the command BEEP accepted that 2 parameters: the frequency and duration of the beep. No envelope or volume, the ZX Spectrum leaving such sophistications to competition.

However the shooting was later corrected on the ZX Spectrum 128 by the addition of a Yamaha AY-3-8912 (identical to MSX, Amstrad CPC, etc.). ]]> Mikey http://forum.zbestshop.com//blog.php?b=1