Category:Sinclair ZX81 BASIC: Difference between revisions
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{{implementation|BASIC}}
Sinclair ZX81 BASIC is the dialect of BASIC resident in ROM on the ZX81 home computer (1981) and compatibles (Timex Sinclair 1000, Lambda 8300, and many others). It was developed by John Grant and Steve Vickers. Today, ZX81 emulators exist for a wide range of platforms and operating systems.▼
ZX81 BASIC is almost a subset of [[ZX Spectrum Basic]], but not quite: the exponentiation operator is spelled <code>**</code> rather than <code>↑</code> (mapped to ASCII <code>^</code>), the unconditional jump and subroutine call keywords are spelled <code>GOTO</code> and <code>GOSUB</code> rather than <code>GO TO</code> and <code>GO SUB</code>, etc. Note also that the ZX81 uses an idiosyncratic (non-ASCII) character set, so that the <code>CODE</code> and <code>CHR$</code> functions do not return the same values as they would on the Spectrum. Floating point operations, some string handling, and low-resolution graphics are supported; colour, sound, user-defined functions, the <code>READ</code>, <code>DATA</code>, and <code>RESTORE</code> keywords, and assorted other features are not.▼
The ZX81 has no moving parts and only four microchips: the 3.25MHz Z80 CPU, an 8k ROM chip containing the operating system and BASIC, a 1k RAM chip, and an uncommitted logic array. Since there is no separate video chip, the CPU spends about 75% of its time driving the display and only 25% doing everything else. This can, however, be controlled under BASIC using the <code>FAST</code> and <code>SLOW</code> commands: <code>FAST</code> blanks the screen and allows the processor to operate at full speed, and <code>SLOW</code> reverts to the default behaviour. Even <code>FAST</code> mode can be slower than some other BASIC dialects running on comparable hardware, because ZX81 BASIC has no integer type: all numeric operations have to be done on 40-bit floats using software floating-point routines.
The original machine's 1k of RAM was shared between the display, the system variables and stack, and the user's program and variables. The Timex-branded model marketed in the United States had a minimum of 2k, as did many clones; an expansion pack was available from Sinclair to increase the RAM to 16k, and expansions of other sizes were produced by third parties.
▲Sinclair ZX81 BASIC is the dialect of BASIC resident in ROM on the ZX81 home computer (1981) and compatibles (Timex Sinclair 1000, Lambda 8300, and many others). It was developed by John Grant and Steve Vickers. Today, ZX81 emulators exist for a wide range of platforms and operating systems.
A PDF version of the manual, <cite>ZX81 BASIC Programming</cite> by Steve Vickers, is available [http://zxnext.narod.ru/manuals/ZX81_Manual.pdf here].
▲ZX81 BASIC is almost a subset of [[ZX Spectrum Basic]], but not quite: the exponentiation operator is spelled <code>**</code> rather than <code>↑</code> (mapped to ASCII <code>^</code>), the unconditional jump and subroutine call keywords are spelled <code>GOTO</code> and <code>GOSUB</code> rather than <code>GO TO</code> and <code>GO SUB</code>, etc. Note also that the ZX81 uses an idiosyncratic (non-ASCII) character set, so that the <code>CODE</code> and <code>CHR$</code> functions do not return the same values as they would on the Spectrum. Floating point operations, some string handling, and low-resolution graphics are supported; colour, sound, user-defined functions, the <code>READ</code>, <code>DATA</code>, and <code>RESTORE</code> keywords, and assorted other features are not.
If you do not have a ZX81 emulator installed on your computer, you can type any of these programs into the [http://www.zx81stuff.org.uk/zx81/jtyone.html JtyOne online ZX81 emulator] and see what they do.
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