Re: Vic Rabbit

From: Marko Mäkelä (
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 

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?


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