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Forth Cartridges
Forth cartridges provided a way to run Forth programming
environments on the Sinclair ZX Spectrum, sometimes with
additional hardware interfaces and machine-code development
facilities. This section documents known Forth cartridges,
their technical features, contemporary descriptions and
published prices where these can be established from
surviving sources.
Features
Original Price
Currah µSource
Currah
The Currah µSource is a ROM cartridge for the ZX Spectrum combining a Z80 assembler, a FORTH 79 interpreter and a debugging monitor. The assembler supports Z80 instructions and can generate standalone machine code. The debugging monitor provides single-stepping, breakpoints and memory manipulation. The cartridge supports the use of assembler and Forth code within BASIC programs and is compatible with the ZX Interface 1 and Microdrives. 1 2
Notes
Contemporary Currah advertising anticipated compatibility between the µSource and other products in the range, including µSpeech. This advertised compatibility has not been independently confirmed. 3
£44.50
2
Price as stated in advertisement. No mention is given as to whether this price includes or excludes VAT, postage or packaging.
Spectrum Forth IO Cartridge
Skywave Software
The Skywave Software Spectrum Forth I/O Cartridge contains 12K of fig-FORTH and provides an RS-232 serial interface using an Intel 8251 and 24 bits of parallel I/O using an Intel 8255. It replaces the Spectrum's BASIC ROM with its Forth ROM, which contains the standard fig-FORTH words alongside additional facilities.4
Features include a Z80 assembler for machine-code Forth definitions; a built-in terminal for modem communications and access to bulletin-board systems; and a machine-code monitor supporting different number bases, simple one-line assembly and disassembly. RS-232 and Centronics printer routines can be used from either Forth or BASIC. The cartridge also supports RAM-disc simulation and Microdrives, and provides access to the Spectrum's colour, sound and graphics facilities from Forth.4
The cartridge is built on a PTH printed circuit board and has a standard DB25 connector for serial I/O and a strip-cable connector for parallel I/O. It is suitable for both 16K and 48K versions of the ZX Spectrum and was supplied with an extensive manual.4
Features include a Z80 assembler for machine-code Forth definitions; a built-in terminal for modem communications and access to bulletin-board systems; and a machine-code monitor supporting different number bases, simple one-line assembly and disassembly. RS-232 and Centronics printer routines can be used from either Forth or BASIC. The cartridge also supports RAM-disc simulation and Microdrives, and provides access to the Spectrum's colour, sound and graphics facilities from Forth.4
The cartridge is built on a PTH printed circuit board and has a standard DB25 connector for serial I/O and a strip-cable connector for parallel I/O. It is suitable for both 16K and 48K versions of the ZX Spectrum and was supplied with an extensive manual.4
Skywave Forth IO Cartridge
£49.95
4
Article states price is for the unit and does not mention if VAT, post or packaging are included in this price.
References
1.
"'Hardware' 'ZX looks at some new add-ons for the Spectrum." - Reviews the Currah µSource programming cartridge, covering its assembler, FORTH 79 interpreter, debugging monitor, practical use and compatibility., ZX Computing, No. February/March 1986, Ray Elder, p. 14
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2.
"Integrated Forth, Assembler and Debug for ZX Spectrum" - Currah µSOURCE advertisement., Your Spectrum, No. 9, p. 89
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3.
"CURRAH µSPEECH Speech Synthesiser for ZX Spectrum" - Advertises the Currah µSpeech speech-synthesis unit, describing its speech output, text commands and compatibility with ZX Interface 1. Also introduces the µSlot expandable motherboard and announces the forthcoming µSource programming cartridge for incorporating assembler and Forth code into BASIC programs. Includes product availability, prices and ordering details., Your Spectrum, No. 9
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4.
"Going FORTH" - Describes the Skywave Software Spectrum Forth I/O Cartridge, detailing its fig-FORTH ROM, RS-232 and parallel I/O interfaces, programming tools, printer routines, Microdrive support and compatibility with 16K and 48K ZX Spectrum models., ZX Computing, No. October/November 1983, p. 61
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External Links
Checking the Currah microsource (U-Source)
(Youtube / Davide Barlotti)
Page Revised: 25/10/2026