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NMI interface for ZX Spectrum

Interfaces used to stop the program and save it to tape.

T-1 interface

This is kind of NMI fix. Extra 2kB ROM replaces #0000..#07FF area. Contents unknown due to EPROM failure. The board has address (Poland of course) written on bottom side:
05-220 Zielonka, skr. pocz. 9/2.

Schematics and board are available for download as Eagle data files. But the interface as designed will not work correctly. It is through one, but the next interface cannot disable the extra ROM, beside strange generator connected to /NMI (not as open-collector). The board is corrected with an extra chip (I haven't checked what's this).

KEY$ interface

Interface of unknown name. BASIC tokens are shorted to make room for extra code (and INKEY$ is shorted to KEY$ - the work name).

This interface is vertical board with through slot. Has 8kB EPROM, 4kB SRAM, 3 TTL logic chips (their names are rubbed off - probably 7400, 7474 and 4bit PROM), a ON/OFF switch and NMI button.

In OFF position, interface is completely disabled. In ON, the EPROM is seen in first 2kB (#0000..#07FF). Writing to 15th kilobyte (#3800..#3BFF), e.g. 14848 (#3A00) address enables extra configuration: EPROM is seen in first 8kB (#0000..#1FFF) and SRAM - in next 2kB (#2000..#27FF). Writing to 16th kilobyte (#3C00..#3FFF), e.g. 15360 (#3C00) returns to normal configuration.

The /ROMCS line is incorectly connected, so next interface with memory will cause memory conflicts. This can be corrected by using resistor and wire connected to the ON/OFF switch. The fix pulls up the /MREQ line on through slot when memory of the interface is use.

Pressing the NMI button displays a rainbow on border. You can press a key:

  • <1> - return;
  • <2> - fast reset;
  • <3> - ?;
  • <4> - save memory in turbo mode, asks "NAME:", then "OK?";
  • <5> - normal reset;
  • <8> - displays "POKE:";
  • <9> - starts copier, menu: Load Save Delete Turbo Reset;
  • <0> - runs monitor/debugger.


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Files for download

key$.zip 49.6kB (2006-06-15 06:40)
Documentation of an interface of unknown name (workname: "KEY$"). EPROM contents, PROM contents and description, schematics and board as Eagle data files.
t-1.jpg 42.2kB (2005-11-11 14:26)
T-1 interface - front view.
zielonka.zip 44.6kB (2005-11-11 14:45)
T-1 interface. Schematics and board as Eagle data files. Missed ROM.

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© 2009-12-28 21:50 Jarek Adamski, http://8bit.yarek.pl