Spectravideo and MSX tapes – straight and inverted signals

A quick reference for dumping Spectravideo and MSX tapes.

In the first image we see the signal coming from a Spectravideo tape side dumped with default settings in DC2N4-LC (i.e. without the “Use halfwaves” option active): this tape side can be dumped without any concern.

Spectravideo tape side that can be dumped with default settings with DC2N

Spectravideo tape side that can be dumped with default settings with DC2N

The second image shows the signal coming from the opposite side of the same tape dumped again with default settings in DC2N4-LC (i.e. without the “Use halfwaves” option active): this tape side at the moment requires re-dumping with the “Use halfwave” option enabled in DC2N4-LC.

Spectravideo tape that requires the opposite edge trigger in DC2N or halfwave dumping enabled

Spectravideo tape side that requires the opposite edge trigger in DC2N or halfwave dumping enabled

In order to produce a TAP file readable by TAPClean in the latter scenario, the dc2n3-conv tool has to be used as per below (as it’s the only tool I make available that supports DMP format 1, the version used when dumping with the “Use halfwave” option enabled):

dc2n3-conv.exe -f -a CrypticCube_SideB.DMP

As I commented earlier today, I am looking at ways to streamline the process in DC2N4-LC GUI clients with some sort of dumping profiles that would expose all dumping modes while avoiding confusion about which option to use in each case.

Bear in mind that the DC2N4-LC commandline client copes with the second scenario without having to enable the “halfwave” option, using the “-r” option:

DC2N4 dump utility, rel 2.3 - (C) 2015-2016 Luigi Di Fraia
Communicates with a DC2N4-LC device to make tape backups

Usage: dc2n4-dump.exe [options] <virtual serial port> <file>

Options:
 -m <machine type> : 0 = C64/Generic, 1 = VIC20, 2 = C16
 -v <video standard> : 0 = PAL, 1 = NTSC
 -r : change first active edge to rising (default is falling)
 -b : set both signal edges as active after first (default is single)

The DMP file thus produced can be fed directly into TAPClean without having to use the dc2n3-conv tool.

Yes, that means that at the moment the commandline client for DC2N4-LC does expose all dumping modes available through the hardware and firmware and is more advanced than the GUI clients 🙂

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2 Responses to Spectravideo and MSX tapes – straight and inverted signals

  1. This note comes from the specification of the CSW format, a format created by a Spectrum demo group but that applies in general to all retro tapes, and is similar to TAP v2 (http://ramsoft.bbk.org.omegahg.com/csw.html).

    “In format revision 1.01 we have introduced a bit to represent the initial signal polarity, which is not important in the Spectrum world but it is for other platforms such as C64. ”

    So, possibly the MSX and the Spectravideo were also insensitive to a polarity switch, and it did not really matter what the polarity was. This would explain why 2 sides of the same tape have opposite polarity.

    • luigidifraia says:

      Similarly, the DMP format Version 1 that I defined a few years ago introduced a bit to represent the active edge used for sampling without halfwaves (or the first active edge when sampling with halfwaves). After all, a number of people came up with reasonable strategies to support different scenarios that we came across and it’s not surprising that there are analogies among these strategies 🙂
      If you look at some of my later posts you can appreciate how DC2N4-LC GUI clients now expose all dumping capabilities of the underlying hardware and don’t require halfwaves for signal with opposite polarity than expected.

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