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Re: zx spectrum next

Posted: Thu Apr 11, 2019 8:41 pm
by rogerjowett

list of speccy clones here but no sales figures and also interfaces for spectrum too no pentagon or general sound neo

Re: zx spectrum next

Posted: Thu Apr 11, 2019 11:00 pm
by Alcoholics Anonymous
rogerjowett wrote:
Thu Apr 11, 2019 7:57 pm
the next has 48KB of video ram which is 16kb more than the zx prism
but it doesnt have 96kb of fast dual ported video ram which would mean it could interlace two screens and double the vertical resolution
The next has several graphics layers - you're speaking about one layer called layer 2 which is 256x192 with 256 colours chosen from a palette of 512.

The 48k memory for layer 2 is not in video ram - it's in the external sram and you can move its location in external sram so you can, for example, draw into a second inactive layer 2 buffer while the active one is displayed. Then switch instantly to this other buffer when ready. So interlace, if the monitor supports it, is possible.

Right now, layer 2 can only come out of the first 512k chip which means out of the first 32 8k pages but it's likely this limitation will be lifted and you'll be able to place layer 2 anywhere in the next's 1792k ram.

Doubling the horizontal resolution of layer 2 would double the memory bandwidth demands on external sram and that would probably cramp on the available bandwidth for the cpu.

There are other layers too.

The standard ula has three 6912-byte display files (spectrum, 128k shadow, timex 2nd) with the usual 256x192 and optional colour upgrade with ulanext. It also has a lores mode which is 128x96 with 256 colours per pixel out of palette of 512. There will be a "radastan" lores mode as well which is still 128x96 but with 16 colours per pixel out of 512 and this one will have two alternate screens in the two timex display files. The timex 512x192 mono mode is there with colours modifiable through palette manipulation. All layers can scroll but the ula currently can only scroll per pixel vertically and by character horizontally. Pixel scroll horizontally requires a rewrite of how the ula fetches pixel data.

Sprites are on a 320x256 surface.

The tilemap is either 320x256 or 640x256 in resolution, scrollable as well. It doesn't use very much memory so you should be able to do quite a few tricks with it by simply writing new tilemap data between frames.

Re: zx spectrum next

Posted: Sun Apr 14, 2019 3:46 am
by rogerjowett
ok i'm afraid i have a lot of questions - mainly based on the articles printed in the crash annuals 2019/18
please can someone help me?
1. copper? what is it what can it do - the crash article said it can drive the 3x ay8912 is this corredct does it do it in parallel with the z80n or is there contention with the z80?
2. 48kb of video ram for 256x192 with 256 colours per pixel - sam coupe had 24kb of video ram for 256x192 with only 16 colours per pixel also sam only has palette of 128 colours whereas neXT (+4) has 512 - but if you look at the high colour demo you can see three yes three screen$ combined to produce multicolour effect - not sure its true 256x384 though yet we are still awaiting confirmation of this try these two links:


3.14mhz80 well really the zx prism is supposed to be clocking 56mhz:

if you manage 28mhz then you are effectively matching the msx trubo r which although it had a clock speed of only 7mhz was in fact an r800 processor with effective 4x speed and 16bit multiplication i think too - you seem to be saying that your synthesized z80n has xtra instructions too what are they and what can they do please?

Re: zx spectrum next

Posted: Sun Apr 14, 2019 3:54 am
by rogerjowett
4. i finally managed to persuade velesoft:

to get a zx spectrum 48K and one zx spectrum 128K program to use the external 1mb ram interface for the sam coupe the great advantage of doing this is that only external ram and the rom run at the full 6mhz - all the internal 512KB ram runs at 3 mhz because the ASIC pauses or contentions the processor when it is accessing video ram - an even more convoluted explanation of this can be found here:

as you can see there is a lot of wait states imposed on mode 1 zx spectrum compatible mode mostly for 48K only as 128K needed the ram bank switching system to be modified too and by hand. We did however manage to get a freescape program running at the full 6mhz and this is what it looks like:

as you can see i was hoping we'd have carrier/battle command and starglider &II by now but I live in retro hope!

Re: zx spectrum next

Posted: Sun Apr 14, 2019 4:00 am
by rogerjowett
oh just out of interest those high colour demos are two 72KB screens technically it is displaying three 24kb screens so that is 24kb more than the next has in video ram terms which is fixed at 48kb i believe - what a pity she doesn't have 96kb as that would mean one out mnemonic to do interlaced video modes - and while you are at it the msx turbo R has 192kb of video ram - so i'm not even sure of what video modes she could manage but i know the msx2 had horizontal scrolling and the msx2+ has vertical scrolling too -
5. am i right in thinking the next has hardware scrolling so what is the dma for i thought the dma could effectively do screen scrolling as that is about all i have seen it do judging by the demos for the MB-02+ high density disk interface and the velsoft datagear DMA both for the zx spectrum 48K:

Re: zx spectrum next

Posted: Sun Apr 14, 2019 4:08 am
by rogerjowett
6.sound? 3x ay8912? well that sounds great but the thing is i can see you need one for zx spectrum 128k compatibility and maybe one for fuller master unit compatibility but we had an saa1099 in sam a 6 channel stereo chip and she couldn't even emulate the SID chip from the commodore 64/128 (by the way the 128 had a 6502 at 2MHz (equivalent to 8MHz80? is that right? and it had a z80 but they were not running in parallel unlike the bbc model b which had a plethora of coprocessor on the 1mhz bus or tube connection i forget which a 6502 at 3MHz and a z80 and even ARM RISC processors that were developed on it before they were used in mobile fones.) -even though the saa1099 can emulate using solar flare from Stefan Drissen a chas n DAVE AMiga MOD player which is 4 channel stereo 8bit sample player - though sam needs a sam dac connected to the comms interface parallel port in order to get 7 bit sample quality:

but i imagine that this uses a lot of the z80b - have you seen the general sound neo? it has a 12mhz z80 and can run flac and mp3 tunes - dunno what sound chip it has though

Re: zx spectrum next

Posted: Sun Apr 14, 2019 4:15 am
by rogerjowett
7. gpio any info?
8. π as in raspberry pie co processor you say well bring it on 1ghz 64bit processor with a graphics processing unit does it have a floating point calculator and a physics processor? in fact what can the GPU on the pie do exactly? how does it compare to the latest nvidia and ati vga cards please? does it have a video encoder chip so that we can encode videos of our next experiences please? - does it even have a gen lock device so we can spread next graphics all over our youtube video uploads that we make with the mpeg 2 encoder chip? if not why not?!

Re: zx spectrum next

Posted: Sun Apr 14, 2019 4:23 am
by rogerjowett
9. pccw benchmarks - well that is a bit unfair - what a pity we cant see the scores for the sam coupe!
and some important words of warning for you... don't miss xmas! sam disk drives when you press reset damage the disks - sam nmi button needed to be debounced for it to work properly and the saa1099 didn't shut up when you pressed reset - so basically the entire machine needed 128KB of internal ram and 128KB of external ram - especially if some of this could be paged in the same way that the zx spectrum 128K +2 (or even +2a/b +3) could ram page for some extra compatibility as there was a plethora of 128K software entering the scene - it would have been exceedingly nice to have external ram pageable into the bottom of ram lmpr a&b instead of hmpr c&d- as this would have meant that cpm would run atr the full 6mhz also if the rom had detected the external ram it could have run BASIC programs from it and then some of its nice routines like GRABbing and PUTing sprites on screen would have been double the performance you can see in a plethora of youtube videos on the sam coupe - well roll on symbiote is all i can say - that is a 50mhz ez80190 with four DMA channels and effectively a 200mhz z80 - cant wait my only problem is to persuade Colin Piggot at quazar to sell me four of them!

Re: zx spectrum next

Posted: Sun Apr 14, 2019 4:24 am
by rogerjowett
and just think the ez80 has a 24bit address bus so that is 16MB of ram and 16MB of video ram so we could finally give the 3dfx voodoo 3500 a run for its money! - dream on!

Re: zx spectrum next

Posted: Sun Apr 14, 2019 4:32 am
by rogerjowett
the other really annoying thing is that the magazine article doesn't do the next graphics or audio justice - more youtube videos please even simple technical examples - the video of elite running at 14mhz was amazing but what if the DMA could rotate and skewy zx - in other words if it could rotate and then skew in all three dimensions that would be equivalent to texture mapping no? it just seems so daft to spend your time developing a device that can only really do 2d hardware features without adding just a few 3d hardware features no i just mean that at 14mhz freescape solid 3d becomes playable whereas it wasn't really playable on the zx spectrum - the games were really 3d puzzle games not really arcade first person shooters - nowadays people want the likes of castle wolfenstein or doom... be nice to see the next have a go at that - the screen shots in crash annual looked a bit samey and just rehashes of old ideas....