From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2002-09-22 21:25:40
Marko Mäkelä wrote:
> But I cannot figure out the commands easily.
Further disassembling revealed that the fast SAVE and LOAD commands are
*S and *L, respectively. The commands must be entered at the beginning
of the command line in direct mode.
The Vic Rabbit format appears to use three different pulse widths. The
pulse widths vary surprisingly much, and there doesn't seem to be too
much error tolerance. The difference of the widest short pulse and the
narrowest medium pulse I observed is only 24 microseconds. The
difference between the widest medium pulse and the narrowest long pulse
is 32 microseconds. I wonder if this format tolerates any tape speed
variations.
The initial sync is CDBBBDBDDBBBBBBBBBBBBBBBBB repeated 1200 times.
(B=short pulse, C=medium, D=long). CD appears to mark the start of a
byte. The tape header is 26 times CDxxxxxxxx where each x is either B=0
or D=1. This header is followed by a C (medium) pulse and 80 times
CDBBBDBDDBBBBBBBBBBBBBBBBB again, followed by one copy of the program,
again followed by a C pulse. Unlike in the normal format, the data
bytes are recorded most significant bit first.
Each block seems to start with a $0f byte. The last two bytes of a
block are a 16-bit sum of the data bytes, excluding the $0f byte and the
checksum bytes themselves.
In the tape header, the file name comes first (16 bytes). Then are two
or three unknown bytes followed by the start and end address of the
program block.
Is this the same format than PET Rabbit? Or am I mixing up Arrow and
Rabbit? Is this format similar to other tape fastloaders?
Marko
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