Search found 74 matches

by kpalser
Wed Sep 16, 2020 9:59 pm
Forum: Sinclair Misc
Topic: ZXForth. Plagerism,clever marketing or something else?
Replies: 14
Views: 526

Re: ZXForth. Plagerism,clever marketing or something else?

I sent some comms to both Bob and David back in May this year to ask if I may include the Forth ROM in my iOS/iPadOS ZX81 app. I did not get a response from either. With Bob I tried messaging his LinkedIn and a gmail account that I found (I didn't try his work email address as I thought that would b...
by kpalser
Tue Jul 28, 2020 10:28 pm
Forum: Hardware
Topic: OUT & vertical sync timing
Replies: 5
Views: 747

Re: OUT & vertical sync timing

Paul Farrow kindly sent me a detailed explanation after I emailed him separately. To save anyone else going to the trouble of answering, it’s about 3 cycles before the end of the OUT instruction. Part way into the port write machine cycle of the instruction. I’ll leave Paul with the honours of expla...
by kpalser
Mon Jul 27, 2020 11:20 pm
Forum: Hardware
Topic: OUT & vertical sync timing
Replies: 5
Views: 747

Re: OUT & vertical sync timing

[/quote]
bola_dor wrote: Mon Jul 27, 2020 4:59 am Perhaps someone at the software or development subforum may help.
I saw you at the Facebook group but I haven't much experience in machine code.. :?
Probably would be more likely to get an answer. I guess I was hoping for more empirical based responses from this channel.
by kpalser
Sun Jul 26, 2020 1:11 pm
Forum: Hardware
Topic: OUT & vertical sync timing
Replies: 5
Views: 747

OUT & vertical sync timing

Hi all, I asked the following on the ZX81 Owners Facebook group but I suspect for techy questions that I’m better asking here. Sorry for the repetition for those of you who are members in both. How many cycles are there relative to the end of an OUT instruction until the ZX81 ends the vertical video...
by kpalser
Mon May 18, 2020 1:58 am
Forum: Hardware
Topic: ZX81 rebuild
Replies: 175
Views: 34459

Re: ZX81 rebuild

I’ve been trying to contact David Husband to ask permission to use the Forth ROM in my emulator. I’m no longer sure who I should be asking. I’ve read the other threads in this group and the above replies regarding the offsets. The fact that David / Skywave Software would have gone on to write Forth ...
by kpalser
Sat Apr 04, 2020 11:35 am
Forum: GAMES
Topic: Tractor Beam - Galaga style game
Replies: 10
Views: 2842

Re: Tractor Beam - Galaga style game

Thanks for making this game so polished. I love the attention to the details which really show in the gameplay!

Kevin
by kpalser
Thu Jan 23, 2020 9:27 pm
Forum: Emulators
Topic: Emulating musical tones using cassette out - help!
Replies: 7
Views: 3452

Re: Emulating musical tones using cassette out - help!

Indeed, the code is used only for the first value in the sound buffer after an IN or OUT. The "newpos" and "subpos" variables are calculated like an integer division and a remainder. So I guess the "subpos" variable smoothes things a bit by not taking the initial value itself, but taking into accou...
by kpalser
Tue Jan 21, 2020 10:06 pm
Forum: Emulators
Topic: Emulating musical tones using cassette out - help!
Replies: 7
Views: 3452

Re: Emulating musical tones using cassette out - help!

Hi Mark, All very well described. Thank you. In a real ZX80 or ZX81, it does not matter if the digital output ends up at a logic high or a logic low ... the output at the mic socket will always change towards the 0V / ground level (silence as far as audio systems are concerned) shortly after any act...
by kpalser
Tue Jan 21, 2020 9:13 am
Forum: Emulators
Topic: Emulating musical tones using cassette out - help!
Replies: 7
Views: 3452

Re: Emulating musical tones using cassette out - help!

Hi Erik & Mark, Thank you both for responding. I see things more clearer now. Some quick thoughts: 5. If the signal is taken to decrease linearly (rather than exponentially) to the silence level, the beeper volume may perhaps be used to efficiently calculate the range of positions in the waveform wh...
by kpalser
Sun Jan 19, 2020 7:45 pm
Forum: Emulators
Topic: Emulating musical tones using cassette out - help!
Replies: 7
Views: 3452

Emulating musical tones using cassette out - help!

Hi All, I’m in the process of adding sound support to my ZX81 iOS emulator app that will be compatible with programs like Kelly Murta's 2005 ZX81 Music Interpreter. The emulator has already had AY support for about 2 years now. To be frank, there are too many holes in my understanding of the mechani...