The TK 90X was the first Brazilian ZX Spectrum clone made in 1985 by Microdigital Eletronica, a company located at São Paulo, Brazil, that manufactured some ZX81 clones before (TK 82C, TK 83 and TK 85) and a ZX80 clones (TK 80, TK 82).
The case was almost the same of the original Spectrum (just a little higher), and the keyboard placement was equal to the original keyboard, except for some additional commands that did not exist in the Spectrums (for characters defined by the user — UDG — in the place of the 'Pound' symbol, and the 'Trace' function in Basic), and included specific Portuguese and Spanish characters such as ç and ñ, as well as accented vowels.
There were two versions: 16 Kb and 48 Kb of RAM. Inside, the same processor: Z80A running at 3.58 MHz, a ROM chip, some RAM chips (old dynamic RAMs 4116 and 4416). Microdigital did some reverse engineering to develop a CMOS integrated circuit (IC) with similar functionality to the original Bipolar IC ULA from Sinclair/Ferranti. The modulator was tuned to VHF channel 3 and the TV system was hardware selectable to PAL-M (60 Hz) as used in Brazil, PAL-N (50 Hz) as used in Uruguay, Argentina and Paraguay and NTSC (60 Hz) as used in USA and many other countries, versatility of features the ZX Spectrum never had ** (Was discover an original ZX Spectrum with NTSC video output in Chile, The ULA is a model 6C011E-3 which generates a NTSC frame size and rate)
Another improvement over the original ZX Spectrum was the sound ouput via modulated RF direct to the TV set instead of the beeper.
Most of the software written for the Spectrum could be run on the TK 90X, but some minor incompatibilities occurred. Only three peripherals were released by Microdigital — a Joystick, a light pen interface and a parallel printer interface. But a Beta disc(48) interface was make by many third party companies called 'C.A.S. disk drive interface' (almost an exact clone from the original Beta disc interface), 'C.B.I. disk drive interface' (with a printer interface included) and 'IDS91' (with a printer interface included made by Synchron) or 'IDS2001ne' (these exclusively compatible only with the TK90X or TK95{no ZX Spectrum use possible},also from Synchron) (and also with a printer interface included) .
The TK 90X was replaced by the TK 95, which had a different keyboard ( professional) and case (identical to Commodore Plus4), not in the rubber format, and exactly the same circuit board and schematics (even marked as TK90X on board, just a few difference in the ROM that made the TK95 more compatible with the original ZX Spectrum). But the same ULA chip, that have only digital logic ports with all the analogic part outside the ULA chip, exactly the same from TK90X. It have been reported that the TK95 had been providing more compatibility with the original ZX Spectrum (i.e. the game Mikie runs only on TK 95, not on TK 90X), but that was reported as a little change in the circuit board (the D1 diode has been disconnected, that made an improvement in ZX Spectrum compatibility) and the changes in the ROM from the TK95. Curiously, some games (fewer) became incompatible due to this modification. TK90X users in Brazil used to make a selectable switch to choose the original TK90X (or TK95) ROM or the ZX Spectrum ROM internally, so they could use almost all ZX Spectrum software.
During that period Brazilians were not allowed to import computers, and therefore the TK 90X became the first affordable color computer of Brazilians and was a big success. Similar status, because it was designed for Portuguese and Spanish language users, was achieved in other Latin America countries, as it was very successfully exported to Uruguay through its local distributor, Ingeniería de Sistemas (but the TK90X exported to these countries were a complete different circuit board and schematics, it also uses an original Ferrati ULA form ZX Spectrum, only externally was identical), and also to Argentina, Chile and Ecuador, where it competed with the Sinclair ZX Spectrum.
Because of its affordability, many commercial software programs were locally developed for the first time for use of small businesses in Latin America to run on the TK 90X, and millions of users had their first computer experience with it.
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