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[aprssig] APRS bit I/O

Rich Mulvey aprs at mulveyfamily.com
Thu Jun 28 18:41:19 UTC 2007


'Scott Miller' wrote:
>>    For output, I would use something like:
>>
>>    SWITCH ID,BIT,STATE
>>     
>
> That's a little verbose.. I was thinking of a more compact, tagged hex
> format.
>
>
>   

   I guess it depends on who you expect to be issuing the commands - if 
I'm sitting at a keyboard, I'd definately want to have something more 
human-readable.  If it's another device spitting out commands, then 
having a format using some sort of bit mask, etc, would be fine.

>>    You can't just assume that if you have multiple devices, you'll 
>> always get their addresses back in the same order
>> when you do a 1-wire ROM SEARCH command.  It's completely arbitrary - 
>> especially if you have other 1-wire
>>     
>
> The SEARCH ROM command is completely deterministic.  It has nothing to do
> with how fast they respond.  Granted, if you add another device you're
> likely to screw up the ordering.
>
>   

   Hmmmm, interesting.  According to 
http://www.maxim-ic.com/appnotes.cfm/appnote_number/187 , you're 
correct.  In practice, I have some long ( 100 yard ) 1-wire nets with > 
15 or so sensors in which I definitely get the ID's back in varying 
orders, using the DalSemi OneWireAPI libs.  Now you have me curious 
about the reason...

- Rich





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