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[aprssig] Tracking and Stacking

Dave Baxter dave at emv.co.uk
Fri Sep 21 08:21:05 UTC 2007


And the venerable Z80 had that too with the DAA instruction (Decimal
Addust Accumulator)
Just that you had to add that instruction after every addition or
subtraction to "Adjust" the blessed thing.

However, there were other creative uses for it too, that I have long
since lost the details for :-(

73.

Dave G0WBX.


> -----Original Message-----
> From: Scott Miller [mailto:scott at opentrac.org] 
> Sent: Thursday, September 20, 2007 8:42 PM
> To: vk4tec at people.net.au; TAPR APRS Mailing List
> Subject: Re: [aprssig] Tracking and Stacking
> 
> 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
> >  
> >  
> >  
> >  
> >  
> >  
> >  
> >  
> >  
> > 
> ----------------------------------------------------------------------
> > ------
> > Andrew Rich VK4TEC
> > vk4tec at people.net.au <mailto:vk4tec at people.net.au> 
> > http://www.tech-software.net <http://www.tech-software.net/>
> >  
> >  
> >  
> > 
> > 
> > 
> ----------------------------------------------------------------------
> > --
> > 
> > _______________________________________________
> > aprssig mailing list
> > aprssig at lists.tapr.org
> > https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig
> 
> 
> 
> 
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