Sinclair ZX80 / ZX81 Forums

When I ported Chopper Drop 3000 to be compiled by MCODER2, the basic program size got bigger than 16K (the generated machine code is inserted into REM in line 1). The the DFILE then moved above 32K (afaik it must be completely moved across the 32K boundary to avoid a crash). BUT THEN THE M1-LOGIC (w...

As fa as I remember I read somewhere (in this forum???) something about the developer of this rom: he told, that the printer code was added in the final development phase just before releasing the ZX80. So maybe some prototype roms contains this code, but not the released roms.

Siggi

Hi there seems to be a problem: this file contains in variable A$ the source code for an assembler file (for ASDIS). The basic program contains only REM. If the program is loaded e. g. by EO and ZX81.rom and I press RETURN, the listing is written to screen and the Zeddy is alive. If the program is l...

Hi Greg this is not a real "inkey" function like in BASIC. The BASIC inkey$ function reads the keyboard "on the fly" and does not wait for a key to be pressed. But this mc stays inside a loop (and does not return) if no key is pressed: @Again Call Keyboard ;Call ROM scan keybd. INC L ;Check for no k...

Connecting a joystick directly to the keyboard lines will overload the Z80 addressbus (driving the keyboard lines), because the capacitive load of the long cable to the external joystick is too high. At least some additional components (transistors or driver ICs) are necessary to drive this long cab...

Do not know Joachim's "Eiermaler"? If not, here it is..

http://forum.tlienhard.com/phpBB3/viewt ... f=2&t=2278

FYI:

Joachim controls his (old and small) lathe with a ZX81:

http://forum.tlienhard.com/phpBB3/viewt ... =2&p=38419

Siggi

McKlaud wrote: ↑

Thu Dec 06, 2018 11:33 pm

And don't forget about 10k resistor between pins 27 & 28.

.. which is not necessary for this use case

Maybe it has been necessary for ram extensions, which had a battery (to write-protect the ram during power-off state) ...

Siggi

Also, if you press the CONT key, your first routine will print another screen of characters... Thats because the JR NZ tests the value of the A Register, you are decrementing BC. No, JR NZ tests the Z-flag, which is part of the F register. It could be set by a lot of instructions (like "DEC C" or "...

See there:
http://www.zx81stuff.org.uk/zx81/hardwa ... emental16K

http://www.zx81stuff.org.uk/zx81/hardwa ... Fitted.jpg

Siggi