Search found 1610 matches

by Andy Rea
Mon Sep 25, 2023 10:20 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97525

Re: Oh no! Not another ULA.

Sorry its been a while... not really sure if its worth pursuing 4X speed any more. 4X speed withg ZXpand ?? probably not... I can't get it stable at all. 4x speed is possible without modifying the main board, we now have 6 wires, 5 you already know about ( extra address lines) the extra wire is conn...
by Andy Rea
Sat Sep 16, 2023 6:24 pm
Forum: Development
Topic: Comparing a (1 byte) variable with a number for equal
Replies: 11
Views: 7243

Re: Comparing a (1 byte) variable with a number for equal

If it were me i would use 0 or 1 ( single bit rather than 2 separate bits) and change the code to something like :- ; variables i_frame .byte 1 ; starting frame main_loop: ; check frame LD A,(i_frame) ; get current frame AND 1 ; bit 0 set ? JP NZ,frame_1_do ; if so... ; ...if not continue here ; do ...
by Andy Rea
Sat Sep 16, 2023 5:52 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97525

Re: Oh no! Not another ULA.

getting somewhere now...

inverse video, Check
inverse border, Check
Double Speed, Check
Quadruple Speed.... Wait what... anyway... CHECK

https://www.youtube.com/watch?v=qy5egYyYEVo

just the good ole POKE .. :lol:

Andy
by Andy Rea
Mon Sep 11, 2023 8:26 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97525

Re: Oh no! Not another ULA.

Been a few days... still here... nothing new has happend... apart from maybe a few more grey hairs....
by Andy Rea
Tue Sep 05, 2023 10:52 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97525

Re: Oh no! Not another ULA.

that's rather interesting, however I don't think I want to modify my memotech keyboard just yet...

right this minute I'm having a bit of fun trying various ideas

regards andy
by Andy Rea
Tue Sep 05, 2023 3:05 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97525

Re: Oh no! Not another ULA.

haven't really tried it on a standard keyboard.. so definitely the memotech at the moment. oh the 20Mhz zx81 had a completely split address and data bus all done inside the cold, so no resistor blocking and digging signal improving signal integrity massivly not to mention improving the amount of swi...
by Andy Rea
Mon Sep 04, 2023 9:59 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97525

Re: Oh no! Not another ULA.

Well i didn't expect that, keyboard reads are screwed up at 13Mhz !!!
by Andy Rea
Mon Sep 04, 2023 5:16 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97525

Re: Oh no! Not another ULA.

@paul... re write protect rom.. so my idea then is ~RAMcs remains untouched... you add ram its your problem to solve addressing ect. ~ROMCS to be selectable option a) as is.. OR option b) the following conditions have to be met. 1) address =< $1FFF. 2) Mreq ( or stretched Mreq ) has to be low. 3) @W...
by Andy Rea
Mon Sep 04, 2023 2:57 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97525

Re: Oh no! Not another ULA.

Moggy wrote: Mon Sep 04, 2023 2:18 pm Just a thought Andy, the older ( classic ) spands use a 2c764 EPROM which is something you may want to check.
my othyer older one had an amd 27C64 150DC the 150 biit been 150ns so its fine also
by Andy Rea
Mon Sep 04, 2023 2:10 pm
Forum: Development
Topic: Oh no! Not another ULA.
Replies: 79
Views: 97525

Re: Oh no! Not another ULA.

About blinkenlight pins: I guess both oscillator pins are unused :?: About BigBang: which content is at address 1001? 255? the orioginaal OSC pin ( pin 35 ) is coonnected.. its function is to use the 18K resistor on the zx81 as a pulldown. it could easily be left unconnected and a pull down placed ...