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Subject: [DPRG] PIC Help
From: Dean Hall dwhall256 at yahoo.com
Date: Tue Aug 7 13:23:03 CDT 2001

> Message: 2
> From: "Kipton Moravec" <kip at kdream.com>
> To: <dprglist at dprg.org>
> Date: Mon, 6 Aug 2001 17:12:34 -0500
> Subject: [DPRG] PIC Help
> Who are all the PIC experts?
> I am bidding a redesign of a little controller that
> uses a PIC16C73A.
> What do I really need to write software for this
> thing?

Their assembler and simulator software are very decent
and available for free.  C compiler demo available for
free, but won't produce a full system as you will

> Are the tools expensive?  Are they free? Do I need
> an in-circuit emulator?

Depends on your project.  I made a caller ID box with
a PIC and used a socket to pop PIC'84s in and out.
If you use a surface mount part, you could still do
ISP to reprogram, assuming you choose a flash part.

The PICStartPlus programmer works very well for DIP
packages.  The one I have does NOT have a header for 
ISP... I don't know if they've fixed that in recent

> I would prefer to write in C, but I am not scared of
> assembler.  Are there C
> compilers?  How much?

The PIC architecture does NOT lend itself nicely
to programming in C.  There are a few C compilers 
available, but I recommend assembly: it's a
small instruction set, and a good set of macros will
go a long way.  Besides, there isn't much code space
to go wasting it with C code.

> Can you download code from a programmed PIC and
> disassemble it?

Yes, if the protection fuse hasn't been blown.
If the fuse is blown, the code is safe from simple 
software dumping, but it could be read by EXTREME
measures (semiconductor physics lab type stuff).
> This thing communicates over a RS-485 bus, but no
> one has the format of the
> data or responses that are sent over the bus.  And
> of course they want the
> new one to be backwards compatible.

get yourself an RS-485 to 232 repeater, 
plug in a PC as a terminal monitor 
and break out the caffeinated beverage of your choice!

BTW: if the protocol is like most, one single bit in
one byte can change the meaning of subsequent bytes,
leaving you without much of a clue.  Tell them it
be cheaper to go on a man-hunt to find the protocol
than it would be to reverse engineer it.

Hopefully, the previous PIC security bit isn't blown
and you can dump the old code and learn!

> The PIC they are using is the PIC16C73A.

Does this mean that you have to use it too?
Or can you pic a newer flash part?
Their newer ones are flash reprogrammable at 5v,
which means you could easily build a reprogrammer.


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