[aprssig] APRS telemetry and the PIC 16F877A

Scott Miller scott at opentrac.org
Thu Jan 25 16:59:19 CST 2007

The OpenTracker code's also out there (it does PWM audio synthesis) and has
the advantage of not requiring any special hardware to do the programming.
The configuration program will take .s19 files straight from the linker and
upload them to the MCU, remapping interrupt vectors on the fly for
compatibility with the bootloader.  You just compile and upload, no need to
pull the chip or switch cables.
I can't remember now which tool it was I used, but it was one of the 'C'
freebies for the PIC.  It didn't support any array size larger than 256
elements, and it had no support for data structures at all.  Really
frustrating for someone who's used to ANSI C.  (got my copy of K&R 2nd
edition here on the desk)


From: aprssig-bounces at lists.tapr.org [mailto:aprssig-bounces at lists.tapr.org]
On Behalf Of Dave Baxter
Sent: Thursday, January 25, 2007 2:57 PM
To: vk4tec at tech-software.net; TAPR APRS Mailing List
Subject: RE: [aprssig] APRS telemetry and the PIC 16F877A

Easy!...  (Reletively at least!)
Google for SOTT, or "Son of Tiny Trak"  The code ports easily to the F877,
and as it's in C, is relatively easy to manipulate.  Somewhere I have one
such already programmed.  I know some people were also looking into using
the PWM system to output the tones.  Likewise, the PWM capture logic to
receive and decode them, for all I know they got it working, or maybe not.
However, as above, the SOTT code goes easily into the F877.  If I can do it,
anyone can!...
The one nice thing about PIC's, is for the same series of CPU, (8 or 16 bit)
the code changes very little between devices in the same family.  Most is
figureing out the config settings, and port naming conventions.  Sometimes
you can have just too many IO functions to choose from.  The F877 is one
such chip.  Just because it has ASYNC/SYNC serial IO, doesnt mean you *have*
to use it.  Hence, code from lesser chips that do all that bit by bit
(Bit/Bang) will still run just fine.
If you go and download the MPLAB toolsuit (for free!)  and the free but
limited version of HiTech C compiler, you'll be OK.  Mind you, by now I
expect the code has been ported to one of Microchip's C compilers.  There
are dozens of others of course.
Other choices, there are several PIC based TNC's about, with freely
available source code, both C and assembler, also both regular packet, and
APRS versions too.
There is nothing wrong with the Atmel chips, but the CPU architecure you
could argue harks backwards in time, though they can be very low power, and
very fast running!  And of course if you have already worked with the Intel
805x series chips, the learning curve could be relatively shallow.
PIC's and RISC archetcture, looking forward by comparison?  You choose,
based on what you have, and what you can get for free!
Have Fun..
Dave G0WBX.


From: Andrew Rich [mailto:vk4tec at tech-software.net]
Sent: Wed 24/01/2007 20:08
To: ozaprs; Aprssig
Subject: [aprssig] APRS telemetry and the PIC 16F877A

I know of the MIM project, but I would like to issue a challenge to the
I have a 16F877A, which has at least 6 A/D and as many ports of logic.
What I want to do is make the 16F877A PIC send APRS telem.
Anyone done it ? Interested in coding it ?

Andrew Rich
Amateur radio callsign VK4TEC
email:  <mailto:vk4tec at tech-software.net> vk4tec at tech-software.net
web: http://www.tech-software.net


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