[aprssig] APRS telemetry and the PIC 16F877A

[Jason Winningham]

On Jan 25, 2007, at 4:57 PM, Dave Baxter wrote:

> There is nothing wrong with the Atmel chips, but the CPU  
> architecure you could argue harks backwards in time,

Atmel has (at least) two architectures, the 8051 and the AVR.  The  
AVR is a fairly modern architecture, designed by some college  
students somewhere in northwestern Europe, IIRC (Norway?  maybe  
Sweden?).  The 8051 is certainly "mature".  (:

> PIC's and RISC archetcture, looking forward by comparison?

Gotta watch the PICs because many, especially the low end devices,  
require multiple clock cycles to execute a single instruction (in  
_spite_ of the fact it's RISC).  A 20MHz 16F628 is actually executing  
instructions at 5M instructions/s, where the AVR family uses a single  
cycle per instruction, so you're getting 16M instructions/s with a  
16MHz device.

If there are free PIC compilers, it's happened since I gave up on  
them.  I'll stick with the AVR all the same.

To keep this on topic, a couple of years ago N4TXI built a tracker  
based on the AVR called WhereAVR.  It generated APRS packets ala TT/ 
OT, but he also implemented a zero crossing detector to _decode_  
packets.  He used it to fire a cutdown mechanism on a high altitude  
balloon by sending a message from his D7.

-Jason
kg4wsv