 MK14 (foreground) with modern reproductions behind | |
| Also known as | MK14 |
|---|---|
| Manufacturer | Science of Cambridge |
| Type | computer kit |
| Release date | 1977; 48 years ago (1977)[1] |
| Introductory price | £39.95 GBP (£314; $430 at 2023 prices) |
| Units sold | 15,000[2] |
| CPU | National SemiconductorSC/MP (INS8060) |
| Memory | 256bytes ofRAM (expandable to 640 bytes) + 512 bytes ofROM |
| Display | 8 or 9 redlight-emitting diode (LED) sevensegment display |
| Input | 20 keykeyboard |
| Successor | ZX80 |
TheMK14 (Microcomputer Kit 14) was acomputer kit sold byScience of Cambridge of theUnited Kingdom, first introduced in 1977 for £39.95. The price was very low for a complete computer system at the time, and Science of Cambridge eventually sold over fifteen thousand kits.
The design was unusual in that it used theNational Semiconductor SC/MPmicroprocessor, which was not widely used in this role. The original design was custom, based on a Sinclair calculator as the main input and output device.National Semiconductor offered them the design of National's IntroKitsingle board computers for free if they agreed to a purchase agreement on the parts, which would be lower than what they could negotiate separately. The original design was dropped in favour of National's offer.
Several upgrades for memory were available, allowing a maximum of 2 KB ofRAM, as well as a variety of other add-ons.
From 1974, Ian Williamson was working at the engineering firm Cambridge Consultants Ltd (CCL) where he repeatedly tried to interest the firm in producingmicroprocessor-basedarcade games. With no success there, he began to consider designing a small computer kit for the growing number of engineers interested in microprocessors. He decided it would have to cost around £50-£60. In 1976, Bywood Electronics released theSCRUMPI kit at £56, based on theNational SemiconductorSC/MP. But the SCRUMPI lacked a keyboard or display, it instead included circuitry to connect it to acomputer terminal, which were very expensive.[3]
Williamson decided to design his own version to address these issues. National had an evaluation system known as the IntroKit that included the SC/MP processor, 256 bytes ofRAM, and several support chips. Among these was a system that interfaced the board to the KBDKit, a handheldelectronic calculator that was used as a basic display and keyboard. But instead of using National's version, Williamson used a calculator chip already being used at CCL, and went looking for a very low-cost calculator to replace National's. This led to the use of a bright red Sinclair Cambridge Memory calculator fromSinclair Radionics as the interface.[3]
By this time, in the spring of 1977, Williamson was offered a job atBritish Leyland, which he accepted. He approached the managers at CCL to take on production of his computer design, but they were uninterested. This led naturally to Sinclair, who already made the calculator he was using and had a long history in selling kits.[3]
Sinclair Radionics had been nationalized andClive Sinclair was losing control of the company. In 1976, he set up Science of Cambridge (originally as Sinclair Instruments) to recreate Radionics' early mail-order kit success. He handed the company toChris Curry, who ran the company single-handedly. Their first product was the kit-formSinclair Wrist Calculator which was moderately successful but relatively low quality. When Williamson approached Sinclair and Curry, they both liked the idea and saw the potential of selling this more advanced kit into the hobby market.[4]
When Curry approached National inquiring about costs for a mass purchase of the SC/MP, National countered by offering them a completely developed computer system based entirely on National's parts. The design combined National's SC/MP Introkit and Keyboard Kit and they offered the resulting design for free, along with some basic software, in exchange for a contract for the parts. Sinclair decided this was a far better deal than what he could arrange using Williamson's design, and Williamson was cut out of further development. Williamson would later be paid £2,000, ostensibly for writing a manual.[4]
It was put on the market at £39.95 plus £3.20 VAT and 40 pence postage and handling. They placed an initial order with National for 2,000 sets, but the low cost resulted in early orders for 20,000. The first systems began to arrive in February 1978, but real production quantities did not begin to arrive for another three months.[5] According to Curry, about 15,000 were sold in total.[4] The name apparently refers to its fourteen components.[6]
The computer is based aroundNational Semiconductor'sSC/MP CPU (INS8060) and shipped with 256bytes ofrandom-access memory (RAM) and 512 bytes ofread-only memory (ROM) as standard. It used an eight or nine digit redlight-emitting diode (LED) sevensegment display although only eight digits were usable, there was also optionalVDU supporting 32×16 text or 64×64 graphics.[citation needed] Input was by a 20-keykeyboard and reset switch. Cassette-based and PROM storage were optional extras; a sound card was not included but a design for one was provided.[7]
The on-board RAM could be increased in two ways; by the addition of an INS8154N RAM/IO chip providing an additional 128 bytes of RAM along with 16 I/O lines, and also a further 256 bytes by adding two 256 × 4 bit RAM chips giving a maximum of 640 bytes on board. These memory spaces were not contiguous in the memory map. It was possible to connect off-board RAM giving a 2170 bytes total.[7]
The MK14 was supplied as a self-assembly kit with the following major components[8]
| Component | Part | Function |
|---|---|---|
| CPU | INS8060N(ISP-8A/600) | SC/MP-II 8-bit microprocessor |
| Clock | 4.433619 MHz or 4.000 MHz | System clock |
| PROM | DM74S571 (512 × 4) ×2 | 1 KB monitor PROM (SCIOS) |
| RAM | MM2111-1N (256 × 4) ×2 (plus ×2 optional) | Onboard static RAM, 256 bytes or 512 bytes |
| I/O | INS8154N (optional) | 128 × 8 RAM and parallel I/O |
| Display | NSA1198/1188 | Eight- or nine-digit magnified 7-segment LED display |
| Keyboard | 20-key keypad | Hexadecimal input |
Other supporting logic included multiplexers, latches, buffers and a regulator.
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