ZX Spectrum 48K and Timex Computer 2048
memory upgrade
to ZX Spectrum 128K compatibility

ZX512 - 256kB or 512kB for ZX Spectrum

Upgrade dedicated only for ZX Spectrum.

The idea was to replace lower 16kB DRAM with the 32kB DRAM taken from upper bank. Then, in upper bank 41256 chips were installed giving 256kB. Next 256kB in 41256 chips could be soldered over the first chips, but with /CAS pin bend up. The video memory was write-only and duplicated.

Port #7FFD worked as in ZX Spectrum 128K and Pentago 512kB - extra banks could be accessible with bits 6 or 7 set. Writing to #5xFD port forced the bit 6 to store 0.

Only one prototipe was made. To limit amount of wires, all logic chips were mounted on a board inserted into ULA socket, while ULA was inserted into the board.

An optional circuit on the board was dedicated to generate "high color" screen, where attribbutes are takes from another 6kB area, like in Timex and Sam. This feature was never tested.

Files for download

stavi128.zip 37.6kB (2005-06-30 15:33)

Documented upgrade made by STAVI (Warsaw, Poland). Dedicated for ZX Spectrum and Timex Computer 2048. Eagle data files.

spectrum_128_artur.gif 123.2kB (2005-06-03 02:15)

128K interface (for ZX Spectrum 48) - 100% compatibile with original ZX Spectrum 128. Originally designed by Artur Muszyński in 1987.

przerobione.jpg 467.2kB (2004-11-28 01:59), uploaded by Mirek

ZX Spectrum 48kB upgraded to 128kB (1990-03-04).

zx512v004.zip 28.7kB (2004-07-02 16:33)

Documenation ZX512 v004. Memory upgrade for ZX Spectrum to 256kB DRAM, where screen memory is duplicated and only banks 5 and 7 are slowed by ULA. Eagle data files.

See also

TC2144

Upgrade to 144kB RAM with compatibility to ZX Spectrum 128K.

4MB RAM upgrade : ZX Spectrum

ZX Spectrum memory upgrade - 4MB RAM (DRAM).