Date   : Wed, 20 Jul 2005 01:23:57 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Re: floppy discs

Tim Fardell <tim.fardell@...> wrote:
> My other "platform of interest" is the ZX Spectrum, and for that, nobody
> bothers to store the original audio - we use .TAP and .TZX format files.
> 
> http://www.worldofspectrum.org/TZXformat.html
See also
http://mdfs.net/Docs/Comp/Spectrum/FileFormat/2_Tape
 
> I don't know if there is a similar format for Beeb tapes?
 
I've been thinking about that myself. The Spectrum .TAP tape
format is the raw data bytes on tape prefixed with a length word.
For example, when you execute the line SAVE "ROM" CODE 0,2 this
will result:
 
       |------ Spectrum-generated data -------|       |---------|
 
 13 00 00 03 52 4f 4d 7x20 02 00 00 00 00 80 f1 04 00 ff f3 af a3
 ^^^^^                                          ^^^^^
length=19 bytes                             length=4 bytes
 
A BBC version would be the bytes sent to the ACIA to be recorded
to tape, in exactly the same format. For instance, doing *SAVE ROM
8000+2 would result in:
 
18 00 2A 52 4F 4D 00 00 00 80 00 00 00 80 00 00 00 02 00 ...
^^^^^
length=24 bytes
 
... 80 00 00 00 00 cc cc
                   ^^^^^
                 checksum
 
04 00 4C 3F cc cc
^^^^^       ^^^^^
4 bytes     checksum
 
In fact, this is exactly the same bytes that would be put in a
sideways ROM for the ROM filing system to use.  Hmmm... ROMFS on
GoMMC anybody?
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
BBC BASIC for the Sinclair Spectrum - http://mdfs.net/Software/Spectrum