ZX81 to ZX Spectrum conversion possible

[bwinkel67]

My only thought is that the smaller of the files called "SLOWLOADER" from 1982 requires the hardware interface and the bigger 1983 version I have titled "slowloader2" is the software only version which sadly I cannot get to load on real thing.

I actually couldn't get the 1982 ZX Slowloader to initially load on my real Spectrum...I think I had used EightyOne's emulated spectrum to save as audio file. I found a tool that does the Tap to Wave conversion sans the emulator and that did create a .wav file my Spectrum could load. So, I'll give that a try and report back...maybe this weekend depending on if I get some time back to my hobby stuff :-/. If I get it to work, where would I share the .wav file?

[bwinkel67]

My only thought is that the smaller of the files called "SLOWLOADER" from 1982 requires the hardware interface and the bigger 1983 version I have titled "slowloader2" is the software only version which sadly I cannot get to load on real thing.

So ZXSlowloader2.tap is actually just an archive file (use 7zip to open it) that conains the SLOWLOAD.TAP file. I looked at the contents and at the start, the ZXSlowloader2.tap had the following, which I recognized as an archive header. Also, it was smaller than SLOWLOAD.TAP (2514 bytes vs 3752 bytes).

Code: Select all

PK  

Where did you find that file? I was looking for the 1983 software-only version online and couldn't locate anything.

Also, looking at the audio file for ZXSlowloader2.wav, it doesn't seem to have a header, so it won't load. If you used the compressed .tap file to generate it then it's just random data.

[bwinkel67]

The slowloader I used in 1997 with my emulator (I converted the code) was from a guy from Holland, name was in a REM line, so is that in one of your versions? I might take a look in the source I have somewhere.

Do you still have that program or know where I could track it down?

[dr beep]

Do you still have that program or know where I could track it down?

Only an altered version to work with my game and probably a print out of the loading code.

Tried a GOOGLE, but not found.

[bwinkel67]

Tried a GOOGLE, but not found

Yes, I tried many a Google to no avail. I also really wanted to see what the device, that ZX Slowloader used, looked like. It says they hooked it to the I/O port so I'm guessing the edge connector. I would guess they wanted to either bypass the audio jack -- or perhaps they couldn't get access to it within their machine code program? Sorry don't know enough about the Speccy to understand how that works.

It's interesting that the EightyOne emulator has no issues with that, so whatever the software is doing, the EightyOne is fine with loading an audio file and connecting its stream to their input routine. Any idea why that would work and does that give a clue what their device is doing? Since they only charged £10 the hardware couldn't have been too complex.

[1024MAK]

Any machine code program can access the tape input (ear) port. It can also access the output (mic). That’s how fast loaders and turbo loaders work. So certainly, it should be possible for a machine code program to load a ZX81 program.

There is one caveat. The machine code must either be running in upper RAM, so a 48K ZX Spectrum is needed. Or be running from ROM (EPROM) (like BASIC) in the ROM area. This is so that good consistent timing can be achieved. Machine code run from contended RAM (the same chips that the ULA gets priority access in order to draw the screen) does not run as fast, and the timing is not consistent. But, for £10, I’m certain that a ROM (EPROM) was not being used.

The hardware? I wonder if it was a dongle to make the program harder to pirate. But that does not make sense if it runs okay on the emulator. And the article that Moggy provided a link to does say that:

The ZX81 cassette is then loaded through a socket on the Slowloader circuit board, rather than through the normal cassette port.

However, on the emulator, code for accessing the hardware is intercepted so that the emulator can provide the correct data to the Z80. So if the hardware is using the same Z80 I/O port and the same bit allocation as the ULA does, then software ran on an emulator will see no difference, and hence will work.

Meanwhile, the same may not be true with a real ZX Spectrum. Especially as there is a difference between the ULAs used in issue one and two boards, and the ULAs used in issue 3 and later boards.

There is one difference between a ZX81 and a ZX Spectrum that I have not mentioned, the filter components (capacitors and resistors) are different between the two. Hence ZX81 tape signals will be seen differently by the ZX Spectrum ULA compared to how a ZX81 ULA sees them. In the software, it may be possible to take account of this. But, this may not have been considered in the first version, hence the need for the hardware board, presumably with an input circuit more like that on a ZX81.

Mark

[Moggy]

The dongle was my thought too as per my earlier post, I have found another magazine link from 1983 (on my other pc at the moment) which carries a review for an "improved " version of slowloader.
No mention of an hardware interface and apparently the improvement lies in how it translates ZX81 specific commands and graphics.

Page 9 of this PDF confirms use of a hardware interface.

https://ia904509.us.archive.org/15/item ... ue8212.pdf

[bwinkel67]

The dongle was my thought too as per my earlier post, I have found another magazine link from 1983 (on my other pc at the moment) which carries a review for an "improved " version of slowloader.
No mention of an hardware interface and apparently the improvement lies in how it translates ZX81 specific commands and graphics.

Would love to track down the improved version, but so far no luck with google.

[bwinkel67]

I've been hunting for the upgraded version. So far nothing, though I did find this advert (Slowloader is in blue because of the search highlight):

I also found a 1987 article reference that says that East London Robotics changed its name to ELR, was putting together the Isis PC compatible, and readers should go up to their stand and buy a copy of ZX Slowloader. Most magazine up to 84 have adverts that show the original at £10. After that it seems to disappear.

I did find a reference in the letter to the editor section in a 1985 ZX Computing Magazine, the editor answers a person inquiring about a ZX Slowloader he'd heard about with: "I'm afraid the Slowloader only worked with Issue 1 and 2 Spectrums, and is now obsolete."

[1024MAK]

Timex Sinclair never released a TS2000 model (they had problems with complying with the regulations), so I can’t imagine that advert running for long. Timex Sinclair instead released the TS2068 in November 1983.

As I said earlier, the cassette tape circuitry in the ULAs for the ZX Spectrum issue one and issue two boards is different to that in the issue 3 and onwards boards. However, all that is normally needed (depending on what the software is trying to do) is a relatively small change to the software. Easy to do if the source code is available. A bit harder otherwise (as it means reverse engineering the machine code).

If you want to know the details of the differences, look at the subsection ‘hardware’ here or read the ‘The ZX Spectrum ULA: How to design a microcomputer’ book (see this site for more details).

Mark