one more question: what is necessary to run the "spectrum rom" SP81.ROM on EO or on a real ZX81?
Using EO I took a 16K Zeddy, enabled WRX and loaded the SP81 rom. But the "Speddy" did not boot
What is necessary on a real Zeddy? 16 K rom (batt-ram in my case) at the "rom side" of the resistors and >= 16 K ram (hires enabled)?
I put the SP81 rom into my Laptop-Zeddy (http://forum.tlienhard.com/phpBB3/viewt ... =305#p1642), where I have 2 banks of 16 KB EEPROM at address 0-16K (big enough to hold the SP81 rom). But it did not work
The reason is (IMHO), that my Zeddy is equipped with a M1-NOT circuit to run m/c above 32K (it has 64K ram).
But the SP81 rom has its DFILE below 16K (at the end of the unused rom space) and jumps to DFILE+32768 to generate the display (an address in range 32-48K). But there the ULA in my Zeddy does not catch the executed code to make the display (because of the M1-NOT circuit). So the display routines don't work
This rom would probably work on a Zeddy without a M1-NOT curcuit. But then m/c above 32K is not possible and Spectrum 48K m/c games won't run above 32K. So the SP81 rom can only be used to emulate a 16K Speccy.
To work on "modern" 64K Zeddies with M1-NOT circuit, the SP81-rom should have the DFILE above 16K (then 48K Spectrum programs with m/c up from 16 up to 48K could be run). But is there any unused space in the Spectrum ram (about 40 byte) to hold a DFILE (e. g. unused printer or other buffers)?
Addendum: here is Mike's old description: http://web.archive.org/web/200707310757 ... .com/SP81/