[Coco] Coco Digest, Vol 45, Issue 32

[L. Curtis Boyle]

On Wed, 11 Apr 2007 06:59:55 -0600, Bob Devries <devries.bob at gmail.com>  
wrote:

> Byte 0 (the first byte of the file) is the preamble flag, which is $00  
> for a binary file and $FF for a Basic file.

Actually, it is $00 for any legitimate chunk of data - the directory entry  
dictates whether it is binary or BASIC.

>
> Bytes 1 and 2 are the length of the data block.
> Bytes 3 and 4 are the load address.
>
> At the end of the file there are another 5 bytes:
> $FF, $00, $00, $xx, $yy where xx and yy are the EXEC address. These can  
> be accessed by using disk basic's random access file commands, as Carl  
> England pointed out.
    A program that goes through (starting with the 1st 5 bytes) can  
amalgamate all addresses by getting the start/length, jumping ahead by  
length bytes, getting the next pre-amble, etc. until the post-amble is  
reached.
>
> Please note that the file can *sometimes* be split into a number of  
> blocks which do not necessarily lie adjacent to each other in memory. If  
> that is the case, a programme would need to step through the file and  
> collate all the lengths and load addresses.
True. Programs that had a "loader" screen (on the 32 column text screen)  
would have a chunk from $400-$5ff, and then the program itself might start  
at $e00.
-- 
L. Curtis Boyle