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[aprssig] Tracking and Stacking

Scott Miller scott at opentrac.org
Thu Sep 20 19:41:35 UTC 2007


Congratulations, you've just discovered packed BCD (binary coded decimal)!

Check out the instruction set for a processor like the 6502.  There are 
instructions in there specifically for dealing with numbers in exactly 
that format.  IBM used to use a lot of BCD, but they got away from that 
with the introduction of the System/360 in 1964.

Scott
N1VG

Andrew Rich wrote:
> I made a simple tracker and realised I was sending full asii characters.
>  
> I now realise that I can stack more into a packet if I use 4 bit stuffing.
>  
> The character "4" and The chracter "7"
>  
> Ascii code for 4 - 0011 0100
>  
> Ascii code for 7 - 0011 0111
>  
> But if you look closely, all you ever want to do is go from 0 - 9
>  
> 0000 - 1111 (0 to 15 in binary)
>  
> So you could go from
>  
> 00110100 (4) 00110111 (7) to 0100 (4) 0111 (7) and get two digits in one 
> byte
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> ----------------------------------------------------------------------------
> Andrew Rich VK4TEC
> vk4tec at people.net.au <mailto:vk4tec at people.net.au>
> http://www.tech-software.net <http://www.tech-software.net/>
>  
>  
>  
> 
> 
> ------------------------------------------------------------------------
> 
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