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Sinclair ZX 81
Computers
Home Computer
United Kingdom
1981
Zilog Z80A
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ZX 81
/media/museum/photos/sinclair_zx81_1s.jpg
/companies/sinclair
Sinclair
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NAME
ZX 81
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MANUFACTURER
Sinclair
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TYPE
Home Computer
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ORIGIN
United Kingdom
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YEAR
march 1981
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BUILT IN LANGUAGE
Sinclair Basic
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KEYBOARD
Touch-sensitive keyboard, 40 keys
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CPU
Zilog Z80A
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SPEED
3.5 MHz
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RAM
1 KB (901 bytes available, up to 64 KB)
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ROM
8 KB
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TEXT MODES
32 x 24 (but 2 lines are reserved for system messages and commands)
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GRAPHIC MODES
64 x 44
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COLORS
Black and white
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SOUND
None
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SIZE / WEIGHT
167 x 175 x 40 mm / 350gr
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I/O PORTS
Z80 Bus, tape, video
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POWER SUPPLY
9V DC , 600 mA (centre polarity = +ve)
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PRICE
Kit :£50 (UK, june 1981) / Ready-built : £70 (UK, june 1981)
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273
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LEFT SIDE
From left to right :\
- UHF TV output,\
- MIC & EAR (Tape interface),\
- Power in (9v DC).
/media/museum/photos/sinclair_zx81_l-side.jpg
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FRONT
/media/museum/photos/sinclair_zx81_front.jpg
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ZX-81
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RIGHT SIDE
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REAR
The only thing here is the expansion port, which can be used for many things...
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TOP
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INSIDE ZX-81
**(1)** Z-80 microprocessor.\
**(2)** Peripherals and memory expansions connector.\
**(3)** RAM memory chips. One or two chips can be used.\
**(4)** 8 Kb. ROM circuit holding Basic interpreter, Input/Output routines and character generator.\
**(5)** Keyboard connectors.\
**(6)** Three jack connectors for the external power supply and tape recorder.\
**(7)** Specialized circuit named ULA in charge of the whole computer's logical management.\
**(8)** TV aerial RF modulator.\
**(9)** Keyboard. Each key can perform up to six different functions.
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"COFFRET INITIATEUR"
This "inititateur" box included a ZX-81 + an ABS chicklet keyboard + a BASIC book + 2 tapes with 10 games. It cost 100 Euros in 1984.
This computer was launched in 1983. It was compatible with the ZX 81 and had the same features (except the 2KB RAM). It had very limited success. The photo shows the DEF with the 'color pack' extension (color + enhanced graphic mode)
The new sale price is $99.95 instead of 149.95
Advert said:
The ZX81 represents the latest technology in microelectronics. More than 10,000 are sold every week. In fact, the ZX81 is the best selling personal computer in the world.
/media/museum/pubs/sinclair_zx81_pub_4.jpg
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KIT VERSION (1982)
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MEMOTECH LEAFLET
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GERMAN ADVERT
Einstein's face probably means: Buy a ZX-81 and you will become a new genius...
Karl_Heinz - www.sharpmz.org
This little black box contains a 2732 EPROM on which you can save & read your data. Maximum amount is 4 KB. Programs stored in the EPROM can then be automaticaly loaded at startup.
The Sinclair ZX-81 may be the most popular computer, but that doesn't mean people like its keyboard. Numerous add-on keyboards and enclosures were manufactured for the ZX-81. This one, from DK'tronics, includes a full-size keyboard with numeric keypad, and an enclosure large enough to fit the Sinclair board and other Sinclair peripherals. Sadly, its price (£45) was almost as much as the ZX-81 computer one.
Advert said:
**MEMOPAK 64K RAM** The 64K RAM extends the memory of ZX-81 to a full 64 KB. The unit is user transparent and accepts such BASIC command as DIM A (9000). It does not inhibit the use of the printer or other add-on units. No additional power supply is required.
**MEMOPAK 32K RAM** The 32K RAM offers your Sinclair a full 32K of directly addressable RAM. Like the 64K Memopak it is neither switched nor paged and enables you to execute sophisticated programs and store large data bases. It is also fully compatible with Sinclair's or Memotech's 16K RAM to give you a full 48K of RAM
**MEMOPAK 16K RAM** The Memopak 16K RAM provides an economical way to increase the capabilities of your Sinclair. And at the same time, it enables you to continue to add on other features with its "piggy back" connectors. It is compatible with the Sinclair 16K or a second Memopak 16K or Memopak 32K to give you 32K or 48K of RAM respectively.
**MEMOPAK High Resolution Graphics** The Memopak HRG contains a 2K EPROM monitor and is fully programmable for high resolution graphics. The HRG provides for up to 192 x 248 pixels resolution.
**MEMOPAK Printer Interface** The Memotech Centronics parallel or RS232 printer interface packs enable your Sinclair to use a wide range of compatible printers. The resident software in the units gives the ASCII set of characters. Both Memopak printer interfaces provide lower case character capabilities. The RS232 interface is also compatible with modems.
Memopak 64K Memory map:\
**0...8K:** Sinclair ROM\
**8...16K:** This section of memory switches in or out in 4 KB blocks to leave space for memory mapping, holds its content during cassette loads, allows comunication between programs and can be used to run assembly language routines.\
**16...32K:** This area can be used for BASIC programs and assembly language routines.\
**32...64K:** 32 KB of RAM memory for BASIC variables and large arrays.
This is a small thermal printer (of very poor quality !). It can print all graphical characters of the ZX-81 and can print 9 lines of text per inch. It was possible to do a hard copy of the screen thanks to the "Copy" command.
This tiny thermic printer can also be used with the ZX-Spectrum.
Excellent emulator emulating nearly all ZX computers (80, 81, Spectrums, Timex, etc.). As well as emulating the machines themselves, numerous addon cards are supported, including hi-res graphics, custom character sets, sound and colour cards.
[**SINCLAIR ZX-81 BASIC PROGRAMMING**](ftp://ftp.worldofspectrum.org/pub/sinclair/books/ZX81BASICProgramming.pdf)written by Sinclair Research Limited / Steven Vickers
compiled/archived by Robin Stuart\
type of document : PDF\
size : 5,2 MB\
source : [www.worldofspectrum.org](http://www.worldofspectrum.org/)
**... READ THE ONLINE VERSION BY CLICKING BELOW :**
[**TIMEX SINCLAIR 1000 - USER MANUAL**](http://www.ts1000.us/usermanuals.htm)written by Timex / Sinclair / Steven Vickers
compiled/archived by Bill Hicks\
type of document : PDF\
size : 3.5 MB\
source : [www.ts1000.us](http://www.ts1000.us/)
**... READ THE ONLINE VERSION BY CLICKING BELOW :**
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THE COMPLETE TIMEX TS1000 & SINCLAIR ZX81 ROM DISASSEMBLY
**THE COMPLETE TIMEX TS1000 & SINCLAIR ZX81 ROM DISASSEMBLY**\
written by Dr. Ian Logan & Dr. Frank O'Hara
compiled/archived by Bill Hicks\
type of document : PDF\
size : 5 MB\
source : [www.ts1000.us](http://www.ts1000.us/)
**... READ THE ONLINE VERSION BY CLICKING BELOW :**
**TIMEX SINCLAIR 2020 COMPUTER PROGRAM RECORDER**\
written by Timex Computer Corporation
compiled/archived by Bill Hicks / www.ts1000.us\
type of document : Online reader
**... READ THE ONLINE VERSION BY CLICKING BELOW :**
The Sinclair ZX 81 was the successor of the ZX 80, and can be regarded as an evolution of it.
The ZX80 could not handle floating point numbers or cassette data files, but the ZX-81 could. The ZX-80 had 4k ROM : the ZX-81 had 8K ROM with 30 additional functions and some instructions to drive the printer. Thanks to a higher level of integrations (the total number of chips in the basic system was 4, against the ZX80's 21), the ZX-81 cost £30 less than the ZX-80. The plastic case was also different. Whereas the ZX-80 looked cheap in it lightweight white case, the ZX-81 was beautifully designed in its black ABS plastic case.
The keyboard was still formed by an underprinted plastic, but this one was made of non-reflective material. Even with this slight improvement it was quite horrible to use, that's why a lot of additional keyboards appeared quickly on the market. Some of the keys sported up to 5 functions, right in the Sinclair tradition, accessible through the "GRAPHICS", "SHIFT" and "FUNCTION" keys.
Here are the functions added over the ZX-80 : ASN, ACS, ATN COS, EXP, INKEY$, PI, SGN, SIN SQR, INT, LEN, LN, TAN, VAL, <=, >=, < >, COPY, DIM A$, FAST, FOR ... TO ... STEP, LLIST, LLIST n, LPRINT, PAUSE, PLOT, PRINT AT, PRINT TAB, SCROLL, SLOW, UNPLOT. Some are quite useful and make you wonder how it was possible to make anything on the ZX-80 !? However, one function disappeared: TL$ which was used to return a string minus its first character.
The ZX-81 could be operated in two modes, SLOW and FAST. The FAST mode which was the only mode available on the ZX-80, only refreshed the display when the system had completed computing, resulting in a painful screen flicker! It was a useful mode when you had to do a lot of calculation without the need to see what's going on all the time on the screen. The SLOW mode, which was indeed quite slooooowwww, behaved like all other computers did, refreshing the screen all the time.
The ZX81 contained only four main chips : the ROM, Z80A CPU, 1K RAM and the Ferranti custom-made chip! It is as simple as that. The machine was assembled by Timex Corporation in their Scottish plant.
This computer was a very great success in Europe in the beginning of the 80's. It was very cheap and a lot of people who now are working on modern PCs or Macs, made their first move on a ZX 81 even though its performance was actually poor!
A very great range of peripherals were developed for this computer, among them : 3.5" floppy disk units, keyboards, high resolution graphic cards, RS232 or Centronics interfaces, RAM expansions, etc... In fact, it was possible to make a pretty good computer from the ZX 81!
The range of expansion options was quite extraordinary. For instance, Memotech created a whole range of modules which would piggy-back, one after another (and using velcro pads to secure to each other and the to the ZX81, as there was no mechanical locking on the edge connector).
So, for instance, you could have additional memory (up to 128k!), high-resolution graphics, disc controllers, joystick controllers, serial ports, and so on.
Popular add-ons also included replacement keyboards - one was a series of mechanical keys which stuck over the membrane keyboard, others involved re-housing the ZX81 inside a new, larger case with a "proper" keyboard.
In fact, the options were - seemingly - endless. Sadly the power supply wasn't particularly stable, so "glitches" were common, resulting in a system reset and the loss of hours of painstaking coding!
yann64andClaude Opus 5.5
b274874139