This wonderful electronic device, also known as the TK-82 was the first “computer” I had contact with.
This computer, of Microdigital Eletrônica Ltda, was one of the first Brazilian home computer anyone could afford. It was a fairly close copy of the Sinclair ZX-80 albeit looking very similar to a Timex TS-1000, the US version of the ZX-81 which was also sold in Brazil.
It was the second computer made by Microdigital, after the TK-80, first attempt to produce a ZX-80 copy. The company will later produce clones of a variety of other popular computers such as the Sinclair Spectrum, Apple II and even Tandy TRS-80 Model III. Actually, Microdigital never produced computers of its own design.
However, the TK-82 wasn’t a mere copy of the ZX-80 but featured several enhancements: two KB of RAM instead of one, a joystick interface, a tone generator and a dual tape transfer speed which could be either 300 or 4800 baud.
Three models were successively launched. The TK-82 with 4 KB of BASIC ROM, then the TK-82S with 8 KB of ROM, then the TK-83 which RAM memory could be expanded up to 64 KB. First models used standard logic chips. They were later replaced by one custom chip, probably copied from the Sinclair ULA.
The TK82 had the ZILOG Z80A processor running at 3.25 MHz, 2 kb SRAM and 8 KB of EPROM with the BASIC interpreter. The keyboard was made of layers of conductive (membrane) material and followed the Sinclair pattern. The video output was sent via a RF modulator to a TV set tuned at VHF channel 3, featuring black characters on a white background. The maximum resolution was 64 x 44 pixels black and white “for graphic plotting”. There were some special characters (shade patterns) useful for games and basic images.
There was one variation, TK82C, which included the SLOW function allowing the video be shown during the processing (the prior version, TK82, ran only in fast mode, so the image was not shown during its processing. In reality, the SLOW function was done by an add-on board that was factory-mounted over the main board.
Although being a ZX81 clone, the TK82C did not have the ULA chip from Ferranti, used in the former. Instead it was manufactured with a dozen of TTL integrated circuits, which resulted in a somewhat large power consumption. This could be noted as the computer’s case used to become quite hot after some minutes of operation.
The data storage was done in audio cassette tapes at 300 bits per second, so “large programs” could take up to 6 minutes to load.
There were some audio cables supplied with the computer for connection with a regular tape recorder.
As the data encoding was entirely done by software, some hacks were made available to allow much faster transfers. Hi-fi recorders were required in order to use the greater speeds with a minimum of reliability.
A 16 KB DRAM expansion was made available and, despite being optional, became a standard item. Soon after, a 48 KB expansion was also released, but due to pricing and the problematic data storage in cassettes, it never sold well.
The TK82C featured a DIN connector for a joystick (in reality, it was wired to the keyboard matrix). Microdigital then marketed an Atari 2600 joystick, accordingly retrofitted to match the DIN connector.
A small printer, indeed a ZX Printer clone was announced for a long time by Microdigital, but was never released.
COMPATIBILITY AND LEGAL ISSUES
All software designed to the ZX81 could run in the TK82C with no problems, and vice-versa. So it was not uncommon to find software distributed in Brazil, that were nothing more than pirated copies of products for the ZX81. However, given the TK82’s popularity, a great deal of original software was developed in Brazil as well.
In 1983, Sinclair Resarch sued Microdigital over copyright violation because of the unauthorized cloning of its product. Due to political trends from that time, the Brazilian court in charge of the case sided with Microdigital.