Search found 880 matches

by siggi
Tue May 14, 2019 10:20 am
Forum: ZX BASIC
Topic: ZX81X2.ROM - and the big bang
Replies: 36
Views: 5087

Re: ZX81X2.ROM - and the big bang: compatibility problem?

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...
by siggi
Mon Apr 15, 2019 9:15 am
Forum: ZX BASIC
Topic: MC INKEY$ replacement
Replies: 2
Views: 364

Re: MC INKEY$ replacement

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...
by siggi
Fri Apr 12, 2019 10:28 am
Forum: Development
Topic: How to Build a keystick port internally to zx81
Replies: 5
Views: 333

Re: How to Build a keystick port internally to zx81

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...
by siggi
Fri Feb 15, 2019 9:51 am
Forum: Hardware
Topic: ZX81 controls a lathe
Replies: 3
Views: 359

Re: ZX81 controls a lathe

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

http://forum.tlienhard.com/phpBB3/viewt ... f=2&t=2278
by siggi
Thu Feb 14, 2019 10:07 am
Forum: Hardware
Topic: ZX81 controls a lathe
Replies: 3
Views: 359

ZX81 controls a lathe

FYI:

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

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

Siggi
by siggi
Fri Dec 07, 2018 10:17 am
Forum: Hardware
Topic: Reversible 16K RAM
Replies: 4
Views: 846

Re: Reversible 16K RAM

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
by siggi
Thu Dec 06, 2018 11:16 pm
Forum: Development
Topic: New to Machine code, help required
Replies: 17
Views: 1735

Re: New to Machine code, help required

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 "...
by siggi
Mon Nov 26, 2018 6:42 pm
Forum: Hardware
Topic: 3K Rampack issues
Replies: 16
Views: 1866

Re: 3K Rampack issues

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 ...
by siggi
Mon Nov 26, 2018 10:20 am
Forum: Hardware
Topic: 3K Rampack issues
Replies: 16
Views: 1866

Re: 3K Rampack issues

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...