I'm looking for the exact tape data format of old SVI-318/328 computers, some kind of whitepapers explaining it.

I've obtained several information from a real tape, but I don't known if the infered rules are correct, if exists any variants, the correct bauds...


Empirically taken from a WAV file the format is:

The bits are codified like this:

  • 0: 4 pulses at ~2400 Hz
  • 1: 4 pulses at ~4800 Hz

Each data block have a pilot tone followed by the data without a pause between them.

The pilot can be codified like 199 bytes with value 0xAA + 1 byte with value 0xFF. These bytes don't have leading or trailing bits and are in MSb format.

And data come codified not using leading bits, and one 0 valued trailing bit. They are also using MSb.

What I need is a confirmation of this coding or not in case there is something missing or not accurate.

  • 1
    Because the SVI line is closely related to MSX which uses CUTS, maybe SVI does also. There's a paper linked from another question here: retrocomputing.stackexchange.com/questions/8540/… Oct 3, 2019 at 8:21
  • 2
    Yes, that isn't the problem. SVI use KCS, like MSX do too. But the pulses codification of pilot/bits/bytes/control bits differs.
    – NataliaPC
    Oct 3, 2019 at 8:52
  • 2
    The things you say definitely sound likely, though possibly not the codification of the pilot tone for purely practical purposes — a lot of people would start the computer saving, then start the tape recording, cutting off the start of the pilot tone. And 0xaa or 0x55 are very common sync patterns after a pilot tone because of the bit patterns. Though start bits are more common that stop bits so that's a bit of a surprise. Agreed that somebody definitely needs to unturf a manual on this.
    – Tommy
    Oct 3, 2019 at 14:24
  • 1
    Did you find this page? wiki.kasettilamerit.fi/wiki/index.php/Spectravideo - it seems to be on a small Finnish wiki whose title translates to "cassette lamers", but the tape format page itself is in English. Jul 18, 2022 at 3:53
  • 1
    Thanks @hippietrail, looks like what I was looking for
    – NataliaPC
    Jul 19, 2022 at 9:55

1 Answer 1


In the absence of any technical manual:

  • SviWav2Cas comes with source to decode sampled SVI3x8 tapes.

  • openMSX can emulate the SVI machines and creates WAV files from SAVE/BSAVE that SviWav2Cas seems to understand.

Maybe save known data from openMSX in SVI mode (say a 1024 zero bytes, or 1024 &hFF bytes) and analyze the WAV files it produces?

(the CAS files from SviWav2Cas don't appear to work with openMSX, though)

  • Sure, that is what I did. But it depends on how faithful that software is. You can use too my conversor from SVI CAS to TSX files and use it with OpenMSX_TSX fork: github.com/nataliapc/MSX_devs/tree/master/TSXphpclass
    – NataliaPC
    Oct 6, 2019 at 11:05
  • 1
    Sounds like you're already doing what you can, then. Developer information seems to be thin on the ground for this almost-but-not-quite-MSX machine
    – scruss
    Oct 6, 2019 at 16:11

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