Richard Le Mesurier wrote:
> I am looking for online reference on programming of the 16f84 on a
> technical level.
>
> How are the DATA and CLK lines used during programming?
> What info is sent to pic for each byte of the hex84 file?
> How do I request the pic to send data back to the PC so I can confirm
> programming?
> What commands does the pic understand being sent to it?

This is all in the "Programming Specification" document.  These are separate
from the data sheets.  Usually one programming spec covers a subfamily of
PICs.  Go to the web page for the particular part you want to program, then
look for "programming specification".  If you look around, you will find
there are many incompatible programming specs.

My ICSP writeup at http://www.embedinc.com/picprg/icsp.htm will give you
some idea of the issues of in-circuit programming you have to think about,
although this document is written for the target circuit designer.

On a separate note, ditch the 16F84.  This ancient relic costs more and does
less than newer parts like the 16F648A or the 16F88, both of which have the
same footprint as the 16F84.

> Due to my problems originally with trying to get a hardware programmer
> running properly, I have decided that an early project will be some
> other form of programmer.

You still need some sort of hardware.  You can't connect a PIC directly to a
PC port and program it.  There needs to be something in between, called a
PIC programmer.  There are two basic catagories of these, those that are
just bare interface hardware, and those that have a local controller.  The
first kind are flaky at best as some things are invariably out of spec.  The
second kind costs a bit more, but is more robust and usually faster.

I make several PIC programmers, all of the second kind.  The EasyProg in
bare board or kit form may be what you want.  Check out
http://www.embedinc.com/products.  Wouter's Wisp628 is also a nice little
programmer from what I hear.

> Maybe someone here has written some programmer software,

Of course, else there wouldn't be any programmers out there.  There is a
large variety of flakeware available for various bare interface programmers.
This kind of software usually tries to wiggle particular port pins in
particular ways, which does work *most* of the time.  Intelligent
programmers implement a command set and thereby use a PC port in its
standard intended way.  Each of those has its own software that drives the
command set from the host.  All my programmers adhere to the same command
protocol specification.  You can download the protocol spec and the full
host software with source code and build scripts from
http://www.embedinc.com/picprg/sw.htm.

Good PIC programmer design is more envolved than it probably appears at
first glance.  I've designed three PIC programmers, each one benefitting
from experience with the previous ones, and I had a lot of general PIC
experience before designing the first one.  To do things right, you really
need variable Vdd, variable Vpp, and a bunch of other features.  There are
no longer single Vdd and Vpp voltages that work for all PICs.

Get a programmer where someone who already has lots of experience with this
stuff has done the work so that you can get on with your projects.
Eventually you will gain enough experience yourself so that you can design
your own programmer if you really want to, but a decent PIC programmer is
not a newbie project.

If you are really really intent on creating your own programmer, consider
having it implement my programmer command protocol.  That way you don't have
to create any host software yourself, and you've got known working tools to
help debug the programmer.


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