Sinclair ZX80 / ZX81 Forums

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

Maybe it does not solve the current problem, but usually each chip should have its own capacitor (around 10-100nF), connected across its power pins to stabilize its power supply. If those C are missing, the board may run (because the logic is OK), but not very stable (because the power supply of a ...

Maybe it does not solve the current problem, but usually each chip should have its own capacitor (around 10-100nF), connected across its power pins to stabilize its power supply. If those C are missing, the board may run (because the logic is OK), but not very stable (because the power supply of a c...