The result looks a little messy, but it worked š The 6116 chip then took care of the first 2K of RAM, and the 4118 took care of the next 1K (actually it would appear twice in the 2nd 2K block of memory space, but that didnāt matter). This was achieved with three NAND gates of a quad NAND 74LS00 chip (see diagram here) using the motherboardās CE and A11 address lines to decide which RAM chipās CE line would be active. Then, I realised that I could piggy-back the original 4118 chip on top of the 6116 (literally, mechanically on top) and get 3K of RAM by ensuring the CE (chip enable) lines were driven separately. Initially Iād replaced the unitās 4118 RAM chip (1K x 8) with a 6116 equivalent (2K x 8, using the same pinout). The photos above reveal a small birds-nest of wiring on the right side of the circuit board. My ZX81 didnāt suffer much by way of expansion (unlike my Beeb) - I limited myself to a more secure power lead, jury-rigged 3K RAM and a rainbow cable bringing out the keyboard connector for an external keypad. My particular ZX81 started with 1K RAM (using a single 4118 chip rather than the earlier design with 2 x 2114 chips), but was eventually upgraded to 2K and then 3K RAM onboard.
More detailed technical specs (and a whole lot more) can be found at Retroaisleās āSinclair ZX81ā website. There was an expansion port at the back for devices such as printers, 16K RAM packs, etc.
#SINCLAIR ZX81 EMULATOR WINDOWS TV#
The entire unit was a single box with membrane keyboard, 9V DC input, TV video output, and cassette audio ports.
#SINCLAIR ZX81 EMULATOR WINDOWS CODE#
It started with 8K ROM and 1K RAM on board, the video output was generated by the CPU (interleaved with executing BASIC and machine code programs). Still works!ÄŖ compact, efficient use of technology for the time, the ZX81 was a 3.5MHz Z80-based computer made by Sinclair Research Limited in the UK. Iāve recently uncovered a variety of cassette tapes from my ZX81 days, along with my old unit itself. Eventually I moved up to a BBC Model B Microcomputer, but the ZX81 definitely whetted my appetite for computing. I spent hours and hours on this thing, learning to program in Sinclair BASIC and Z80 machine code to squeeze the most out of my 1K (later 3K) of RAM.
I purchased a ā Sinclair ZX81 Microcomputerā not long after it hit the market in the early 1980s - my first real home computer.
0 kommentar(er)
