has anyone though of converting a load of zx spectrum titles to the zx81?
has anyone though of converting a load of zx spectrum titles to the zx81?
for instance dizzy would b cool. i know the zx81 can do hi res, so y not?
Re: has anyone though of converting a load of zx spectrum titles to the zx81?
Hi, welcome to the forums.
Generally ZX81 games happens because of what people want to develop, so if you wanted to learn Z80 to make a Dizzy-inspired game then this is the place to be.
Regards,
Shaun.
Generally ZX81 games happens because of what people want to develop, so if you wanted to learn Z80 to make a Dizzy-inspired game then this is the place to be.
Regards,
Shaun.
Re: has anyone though of converting a load of zx spectrum titles to the zx81?
cant some of the code just b ported directly across?
Re: has anyone though of converting a load of zx spectrum titles to the zx81?
I have no experience with ZX spectrum but have read in these forums that it's quite similar to ZX81 and that you only need to change the graphic routine to port a game (if the game is monochrome)
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Re: has anyone though of converting a load of zx spectrum titles to the zx81?
The ZX81 and ZX Spectrum have a lot of similarities, but also some significant differences.
The basic ZX81 with 16k byte RAM pack (or equivalent) has RAM between 16k and 32k, the same as a 16k ZX Spectrum. They both use a Z80 CPU, but the ZX Spectrum runs slightly faster at approx 3.5MHz compared to approx 3.25MHz for the ZX81. The keyboard electronics hardware is similar.
The ZX81 has no sound.
In terms of a high resolution graphics display, yes the ZX81 can display the same as the ZX Spectrum. However, unlike the ZX Spectrum where all the CPU has to do is put the screen data into screen memory (display file), the ZX81 CPU also has to help draw the picture on the screen as the ULA in this machine cannot produce a video picture on it's own. By this, I mean the CPU and the ULA work together to get each byte of the display file and then the ULA converts the byte that the CPU has just fetched to a serial bit stream to send to the display device (monitor/TV). The drawing of the video picture takes up a significant amount of the CPUs time. Because the CPU is used for the video picture generation, timing in the ZX81 is critical.
Mark
The basic ZX81 with 16k byte RAM pack (or equivalent) has RAM between 16k and 32k, the same as a 16k ZX Spectrum. They both use a Z80 CPU, but the ZX Spectrum runs slightly faster at approx 3.5MHz compared to approx 3.25MHz for the ZX81. The keyboard electronics hardware is similar.
The ZX81 has no sound.
In terms of a high resolution graphics display, yes the ZX81 can display the same as the ZX Spectrum. However, unlike the ZX Spectrum where all the CPU has to do is put the screen data into screen memory (display file), the ZX81 CPU also has to help draw the picture on the screen as the ULA in this machine cannot produce a video picture on it's own. By this, I mean the CPU and the ULA work together to get each byte of the display file and then the ULA converts the byte that the CPU has just fetched to a serial bit stream to send to the display device (monitor/TV). The drawing of the video picture takes up a significant amount of the CPUs time. Because the CPU is used for the video picture generation, timing in the ZX81 is critical.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: has anyone though of converting a load of zx spectrum titles to the zx81?
The Spectrum is built upon a ZX81, which in turn is an upgraded ZX80 with a ULA as I understand it.
You'll have to look at what options for extra memory are available for real hardware, so consider that the Spectrum has ~40K free to the programmer for the 48K model (where as the 16K Spectrum has ~8k to the programmer). The ZX81 has ~15K for a typically expanded machine. It depends on how much more memory - if anything - will be required for the high resolution solutions available, something that I've not looked into.
Limitations are easily broken with emulation and modern upgrades, so this is where you'll have to find out more. There is a lot of knowledge here so feel free to ask more technical questions.
Regards,
Shaun.
Re: has anyone though of converting a load of zx spectrum titles to the zx81?
If you want to do it, it is better when you have the source.
I have converted my "Shogun" from the ZX Spectrum to the ZX81.
http://minigamecompo.weebly.com/2k-page.html
Problems I met, but I knew in advance:
1) IX and AF' can't be used. I had to alter some routines.
2) the game uses the RST16 from the ZX Spectrum. This had to get its own printroutine : CALL RST16
3) Characterset is different. All printed text needed alterations.
4) colour had to be replaced by something else.
5) write your own hiresdisplayroutine.
6) speed can be an issue since the ZX81 has a slower Z80 and does a lot screentime.
I have converted my "Shogun" from the ZX Spectrum to the ZX81.
http://minigamecompo.weebly.com/2k-page.html
Problems I met, but I knew in advance:
1) IX and AF' can't be used. I had to alter some routines.
2) the game uses the RST16 from the ZX Spectrum. This had to get its own printroutine : CALL RST16
3) Characterset is different. All printed text needed alterations.
4) colour had to be replaced by something else.
5) write your own hiresdisplayroutine.
6) speed can be an issue since the ZX81 has a slower Z80 and does a lot screentime.
Last edited by dr beep on Wed Aug 30, 2017 9:00 am, edited 1 time in total.
Re: has anyone though of converting a load of zx spectrum titles to the zx81?
To compare the games: both ingame screens
Re: has anyone though of converting a load of zx spectrum titles to the zx81?
Yes, you'r true...
No Basic compatibilities : multi-commands line allowed on the spectrum!
spectrum:
10 print:print:print
ZX81:
10 print
20 print
30 print
You had to convert the Basic programme to a text file, add lines and delete all illegals commands/functions...
And build a P file from text file, and convert it in a wav file...
Or rewrite it on a ZX81!
->The ZX81 to Spectrum is ok...
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
Re: has anyone though of converting a load of zx spectrum titles to the zx81?
Of course, one must remember that the best ZX81 titles are ZX81 exclusive titles. It's better to build from within the limitations than to down-scale from the Spectrum to the ZX81.
Regards,
Shaun
Regards,
Shaun