Re: Zx81
 

I think the flight simulator one is in the cassette I have-it’s an old cassette with a tiny insert explaining all the games. I’m amazed how speedy the Asteroids game plays. Was a little confused at first when the starship kept changing from 0 to other numbers as you turn the craft around to fire at the incoming asteroids! Thought something was wrong!

Re: Zx81
 

Can’t seem to find 3D Monster Maze anywhere.

Re: Zx81
 

Not sure whether you mean you can't find an original tape for sale - it's probably the one that people are least likely to sell, but from what you have written earlier you may already have some material found in .TZX or .P file format so I assume you have a way of converting those to audio playback format.

Have a look around on this site, where there is a lot of useful archived material including books, various utilities, and other things.

http://www.zx81stuff.org.uk/

For example, here:-

http://www.zx81stuff.org.uk/zx81/tape/3DMonsterMaze(NGS)

I personally also had great fun with 'Seawolf', which is a kind of early forerunner of 'Silent Service', the submarine simulation.

http://www.zx81stuff.org.uk/zx81/tape/SeaWolf(Newer)

Re: Zx81
 

That’s great-thank you. No I don’t have any conversion software yet-will search for some. What I need is something to give me a simple wav format. I have some software to do that for the PET but can’t get it to work on Windows 7 even though it said it would run. I’ll keep searching!

Re: Zx81
 

There is a utility to convert .P and .TZX files to audio files on the site I linked to in #223.

http://www.zx81stuff.org.uk/zx81/tap.../overview.html

Re: Zx81
 

Thank you for this-Ill check it out.��

Re: Zx81
 

If you see anything you think might be interested on that site, have a go at it by pressing the 'play' button on the page for the software title concerned and you can test drive it using the website's built-in full speed online emulator. All very nicely done.

I'm fairly sure I have that converter software installed on one of my XP machines so if you have trouble getting it to work let me know via PM which ones you want and I'll have a go at converting them for you.

Re: Zx81
 

Thank you! I’ll take a look.

Re: Zx81
 

3D Monster Maze was *the* game back in the day and I understand that in more recent years young retro gamers have come to appreciate it too. Some play it with huge screens and describe the moment the T-rex appears on screen as "pants wetting".

Other games I'd specifically recommend for the ZX81 are the more recent "Mayhem"
https://www.homebrewlegends.com/zx81-mayhem/

I still get kicks out of "Perilous Swamp" from the "Fantasy Games" cassette, and Catacombs another JK Greye title.

Artic's Galaxians was great
Mazogs

Re: Zx81
 

I cant remember if you could buy it as a kit or made up like the ZX80?
Bought mine ready made direct from Sinclair originally , and then bought another from WHSmith a while after .

Re: Zx81
 

Yes, mine (My ZX81) was a kit.

Re: Zx81
 

I made mine from a Kit which guess what - didn't work! So had to go back to Sinclair - their diagnostic helpline asked me to put my finger on the ULA and I said "Ouch its hot" - so he said - hmmm not that then. Turns out the Z80 was faulty so they repaired it FOC but, it was several agonising weeks waiting for it to come back, just reading the manual. I still remember the feeling and love looking at my original manual with its pencil notes.

Re: Zx81
 

And they were great manuals, weren't they? I notice the NEXT manual looks to be of similar quality.

Had to laugh out loud at the anecdote regarding the warm ULA, operating temperature never has been any guide or clue to whether a Sinclair ULA is OK or not. If the ULA is red hot and the computer is working, the ULA is OK. If it's red hot and the computer is not working, the ULA might still be OK. No wonder they caved in so often.

Re: Zx81
 

For those interested , I've found an emulator based around the zx spectrum 48K & 128k models. It's called BASin, and the package contains a lot of useful information. Nice to play with to get back to the old days .

Re: Zx81
 

I still can't believe all the time I spent writing machine code, typing it in as hex, saving it, then running it and it crashing and having to load it back in from tape again, modify, try again. A 16K program took about 20 minutes to load! The worst thing was there was no way to verify, and often it would wait until the end of the recording before deciding there had been a read error somewhere and crashing. But I persevered. I managed to write the first level of the arcade game Scramble. A lot of work.

For some while now I've had an ongoing off/on project of writing a full screen, full feature version of Space Invaders for the 1K ZX81 (I use an emulator these days for reasons stated above). Haven't managed it yet. It's nice to have an unattained goal. I was very fond of my ZX81.

Re: Zx81
 

I remember someone created a VERIFY routine for the ZX81, but I'm afraid any copy I had is long since gone by now. The code simply sat in the usual REM statement in the first line of the program, and a successful SAVE could be VERIFYed by evaluating USR 16514.

It shouldn't actually be very hard to recreate, with access to the ZX81 ROM disassembly. You would have to base it on the LOAD routine in the ZX81 ROM; but instead of storing the byte read from tape into memory, just CP it against the byte at that location. Note the first few bytes of the file are system state, and could have changed since the program was SAVEd! It should be obvious from the code what is what. You can bomb out with an error code straight away in the event of a mismatch, or signal no error if you made it all the way to the end of the file.

If a 1K invaders game is going to be possible, you'll have to use nearly all the available RAM for the screen display and so pull optimisations like increasing the score in place in display memory and stomping on anything you aren't going to drop back to BASIC and need again.

Re: Zx81
 

Well, someone famously did manage to write a pretty respectable 1K chess game although the game board itself was shunted into one corner of the screen.

Re: Zx81
 

Well I don't think there's much call for a verify routine in this day and age, even a ZX81 enthusiast wouldn't actually develop on the actual hardware any more. I wish I'd had one in 1981 though!

The 1K Invaders thing has been through several ideas involving custom screen buffer routines (in fact this thread just started me thinking of another approach) but please don't help me, it's something I like to contemplate on and off and maybe one day actually achieve.

And nowadays at least I have an assembler on PC to write it with!

Re: Zx81
 

Okay, without encroaching on your ideas for how to tackle the programming project, how will you load the finished code onto a real ZX81? Just interested.

I don't even know how developers did that back in the day, I assume it was rather unlikely that professional devs wrote on the actual machine (although I'm sure the one-man back bedroom programmers did, in the early days).

Re: Zx81
 

Well the easiest way without any hardware would be to play it into the cassette port from a WAV file :)

I don't know myself how people did it in the day. IIRC I think I read that Nine Tiles, who did Sinclair's software development, had some sort of emulator running on a minicomputer. There wasn't much of a commercial scene for the '81 and other than Sinclair themselves it was pretty much a cottage industry so they would've used their own proprietary solutions I would guess. For instance you could burn code onto EPROMS, or map some kind of interface into the spare memory map, that sort of thing.

Wouldn't be surprised if some of the few were doing the same as me, saving onto cassette and hoping for the best. With the exception of the legendary 3D Monster Maze, even the few 3rd Party commercial programs were pretty, um, basic.