It's in all 128 models, but the behaviour is slightly different. The original 128 and +2 lock the paging mechanism, the +2A and +3 do the equivalent of USR0 instead
Search found 1409 matches
- Sat Apr 27, 2024 8:16 pm
- Forum: Programming
- Topic: USR0
- Replies: 9
- Views: 1218
- Thu Apr 25, 2024 9:00 am
- Forum: Programming
- Topic: jump if signed 16-bit number is >0, <=0, fastest code
- Replies: 34
- Views: 487
Re: jump if signed 16-bit number is >0, <=0, fastest code
I suspect the easiest way is to check for 0 first, by just ORing the bytes and checking the Z flag. Assuming it's not 0, it's just a single bit test of the relevant sign bit. Should be easily adapted to any size of integer. Whether it's the fastest sort of depends on how you're measuring it, since t...
- Wed Apr 24, 2024 9:12 pm
- Forum: ZXDB Discussion
- Topic: Music files in SC and other sites. Permission affair.
- Replies: 11
- Views: 476
Re: Music files in SC and other sites. Permission affair.
I think a message stating they are only for personal use and not to be reused in your own software without permission etc (as well as respecting authors who do not want them separate) should really be enough. Ultimately there is a long history of people ripping AY tunes and using them elsewhere and ...
- Fri Apr 19, 2024 8:37 am
- Forum: Other Retro Stuff
- Topic: Any CPC Wiki forum users?
- Replies: 4
- Views: 170
Re: Any CPC Wiki forum users?
Yeah, was working fine for me this morning. Bit slow occasionally but that's not abnormal.
- Thu Apr 18, 2024 8:38 am
- Forum: Games/Software
- Topic: Something I noticed about Renegade 3
- Replies: 12
- Views: 517
Re: Something I noticed about Renegade 3
Those rating it >5, how do you rate Double Dragon? I've never entirely understood the hate DD on the Speccy gets. Me and my sister loved it as kids, as one of the few co-op games we had. The multiload was a bit punishing on 48K but it was still fun. I can understand that the graphics have a differe...
- Wed Apr 17, 2024 2:43 pm
- Forum: Games/Software
- Topic: Something I noticed about Renegade 3
- Replies: 12
- Views: 517
Re: Something I noticed about Renegade 3
Without the Renegade title and without the ridiculous time limit, it'd be a solid 6/10 budget game. With both of those and at full price, it fully deserved to be slated.
- Sun Apr 14, 2024 1:52 pm
- Forum: Games/Software
- Topic: The best playable demo of a budget game on a YS/Crash/SU covertape: vote
- Replies: 7
- Views: 356
Re: The best playable demo of a budget game on a YS/Crash/SU covertape: vote
I loved Dizzy and his many sequels, so they'd easily take the top spot, except I'm applying my own arbitrary rules again that I actually have to remember the demo and not the full game so they're out of the running. So with those completely nonsense rules in place: 1) Steg the slug - an underrated g...
- Sun Apr 14, 2024 11:15 am
- Forum: Programming
- Topic: Bank switching issue
- Replies: 32
- Views: 1128
Re: Bank switching issue
also note that by destroying sysvars you won't be able to use +3DOS. you need to call ROM interrupt handler to eventually turn drive motor off, and it uses some other sysvars too. tbh, i never bothered to get rid of sysvars, and i don't think you need to. ;-) hey, you wasted 257 bytes on interrupt ...
- Fri Apr 12, 2024 9:10 pm
- Forum: Sinclair Miscellaneous
- Topic: New forum game -- Spectrum graphics in the real world?
- Replies: 145
- Views: 6669
- Fri Apr 12, 2024 12:56 pm
- Forum: Programming
- Topic: Data prior to the default UDG bank
- Replies: 15
- Views: 322
Re: Data prior to the default UDG bank
Would popping the registers off the stack between levels help? If you're writing "clean" code, the number of things you PUSH and POP should always align (not that CALL is also a PUSH and RET is also a POP) in such circumstances. So you should be reasonably confident that your stack is in ...
- Thu Apr 11, 2024 6:28 pm
- Forum: Hardware
- Topic: Purely theoretical ROM swap
- Replies: 7
- Views: 287
Re: Purely theoretical ROM swap
I mean, you could probably find out exactly by just supplying a zx81 ROM image into a spectrum emulator. It won't be very useful regardless, because the zx81 ROM will have absolutely no idea how to drive the screen or poll the keyboard, it'll just fill RAM up with garbage and sit around waiting.
- Tue Apr 09, 2024 7:37 am
- Forum: Other Retro Stuff
- Topic: Lara Croft voted most iconic character ever
- Replies: 42
- Views: 961
Re: Lara Croft voted most iconic character ever
It's been also said about Master Chief earlier, but tbh I'm not sure where does this notion come from. Both these characters have very strong identity, (visual, at least) and the fact that they don't say much or that MC is wearing a helmet doesn't stop me (and clearly a lot of other people) from re...
- Mon Apr 08, 2024 5:40 pm
- Forum: Games/Software
- Topic: The best playable demo of a full price game on a YS/Crash/SU covertape: vote
- Replies: 45
- Views: 856
- Sun Apr 07, 2024 10:17 am
- Forum: Games/Software
- Topic: The best playable demo of a full price game on a YS/Crash/SU covertape: vote
- Replies: 45
- Views: 856
Re: The best playable demo of a full price game on a YS/Crash/SU covertape: vote
It's very hard, so I've tried to stick to games I remember playing the demos of back in the day and enjoying. Which, to some extent, excludes those I bought the game of because I'll have forgotten the demo but hey ho. 1) Dominator - I remember loading this one, lots. As a massive R-Type fan I loved ...
- Sat Apr 06, 2024 2:37 pm
- Forum: Other Retro Stuff
- Topic: Lara Croft voted most iconic character ever
- Replies: 42
- Views: 961
Re: Lara Croft voted most iconic character ever
I may have shot down my own arguments here. Just asked my girlfriend - who is not a gamer unless you count The Sims or those rollercoaster games - to name a videogame character. Without the slightest pause: "Lara Croft". Can't say I'm surprised, I think some people here have a very skewed...
- Thu Apr 04, 2024 9:24 am
- Forum: Programming
- Topic: Bank switching issue
- Replies: 32
- Views: 1128
Re: Bank switching issue
you prolly have the stack somewhere around $FF00, or something. so when you switched the banks, the window [$C000..$FFFF] moved to another memory region… and your stack stays in the old one. ;-) just remember that memory area [$C000..$FFFF] is affected by switch, and design your code around that. I...
- Wed Apr 03, 2024 8:28 am
- Forum: Showcase your work!
- Topic: Abersoft fig-Forth Recompiled
- Replies: 108
- Views: 2538
Re: Abersoft fig-Forth Recompiled
this will limit the ways to use the system. the idea is that you can move the sprites anywhere in your code, when you want it, not when the system wants you to do it. you command — the system obeys, not vice versa. ;-) Doing this in interrupts will make the code exponentially harder to use. Because...
- Tue Apr 02, 2024 3:18 pm
- Forum: Programming
- Topic: Bank switching issue
- Replies: 32
- Views: 1128
Re: Bank switching issue
I bet you still have interrupts enabled? If you do, you need to update the relevant system variables before you switch banks. If you don't do that, there is every chance the system will sweep in when you're not looking, do some stuff and then "restore" the correct banking as per the variab...
- Sun Mar 31, 2024 7:05 pm
- Forum: Programming
- Topic: Zilog's Z80 opcode choice
- Replies: 20
- Views: 527
Re: Zilog's Z80 opcode choice
Honestly I don't think it's the prefixes I'd be bothered about. If I wanted to tweak the Z80 design, removing the need to re-read instructions like LDIR would've been where I'd go next. And maybe redesign instructions like OTIR to be better suited to a 16-bit IO range (use DE as the destination rath...
- Sun Mar 31, 2024 1:29 pm
- Forum: Programming
- Topic: Zilog's Z80 opcode choice
- Replies: 20
- Views: 527
Re: Zilog's Z80 opcode choice
DEC SP/INC SP are silly instructions too. It would be loads better if it decremented/incremented by 2, changing by 1 has no use I can think of, since you always push a word to the stack. If it incremented by 2 it would just be like discarding the value on the top of the stack (I usually use POP AF ...
- Sat Mar 30, 2024 11:14 pm
- Forum: Programming
- Topic: Zilog's Z80 opcode choice
- Replies: 20
- Views: 527
Re: Zilog's Z80 opcode choice
Well, the decision was mostly made for them. A design goal of the Z80 was to be able to run all 8080 code at a binary level, so you couldn't really just swap out less used instructions even if you wanted to. Whether that was really necessary is a different question I suspect the actual instruction s...
- Thu Mar 28, 2024 1:18 pm
- Forum: Games/Software
- Topic: Starglider being used to gunge children on telly in 1987
- Replies: 8
- Views: 697
Re: Starglider being used to gunge children on telly in 1987
Yeah, I've heard that said and I didn't actually mean to drive down there, it's just that an incident with my car meant I had to stop in Norwich city centre for a while and when I resumed going to my actual destination, I saw myself heading down that very road. Even though it was a Thursday afterno...
- Thu Mar 28, 2024 9:49 am
- Forum: Games/Software
- Topic: Starglider being used to gunge children on telly in 1987
- Replies: 8
- Views: 697
Re: Starglider being used to gunge children on telly in 1987
Almost certainly Amigas. From what I hear of Barcadia, you have to pay £10 for a bunch of American quarters, which gets you about 10 goes on the arcade machines, it's also located on probably the worst street for dealing with drunk clubbing types. Meanwhile, five minutes away there is an arcade in t...
- Wed Mar 27, 2024 7:38 pm
- Forum: Hardware
- Topic: Whitby Computers Spectrum Simulator for C64
- Replies: 1
- Views: 481
Re: Whitby Computers Spectrum Simulator for C64
Ah, so a hand coded reimplementation of the Speccy ROM in 6502. I'd have guessed it had to be something like that to function at any kind of speed, actually emulating a Z80 would've been a very tall order. Impressive that he also got it loading actual ZX tapes via the C64's slightly weird tape syste...
- Tue Mar 26, 2024 8:36 am
- Forum: Sinclair Miscellaneous
- Topic: DenOfGeek : The games that defined the Spectrum
- Replies: 31
- Views: 1026
Re: DenOfGeek : The games that defined the Spectrum
There are also Dizzy (Amstrad CPC) If you look at the internals of Dizzy, it's pretty obvious the primary target platform was the Spectrum. The CPC version stores all the colour numbers in Spectrum format and then remaps them onto its 4 colour mode (this is why there are no blue background objects,...