The rom loader is a method of re-programming the PIC without a programmer and in
circuit.

The newer flash chips (16f87x) have the ability to write to their own program
memory.  Other flash chips (16f84, etc) could only write to a special data
memory.

Since these newer chips can write their own program memory, then we can install
a tiny program in the chip which will act as a loader for the program.  In other
words, connect the chip to a computer and send the new program code straight
over.  No programming voltages, no special sockets, and easy to accomplish
remotely (over telephone, radio, internet, etc) so you don't have to be
physically present to re-program a chip.

Generally the setup is as follows:

A pin is set apart such that when the PIC powers up, it checks this pin.  If the
pin is in a pre-defined state (low) it starts the user program (the program
which was last stored in the chip) if the pin is in the other state (high), it
starts the bootloader code, which accepts commands to read and program the user
program area of the chip.  Once programming is complete the bootloader either
resets the chip, or starts the user program.  One could also provide options
inside the user program which will call the bootloader so you don't have to be
at the hardware setting/clearing pins.

An example of where this might be useful:
Datalogging equipment.  Instead of having a chip which has set functions (which
really means set limitations) you can use, you can reprogram the entire chip to
do some data processing as well as logging.  You could update the program as
your research continues and you discover that your data isn't complete, and you
need to change some parameters remotely.

Home automation, process control industry, anywhere where functionality might
need to be upgraded.

Rapid prototyping, making devices which need to be deployed yesterday with a few
basic functions, but need to provide more complex functions ASAP.  (or following
software company models of releasing buggy product, and sending out service
packs, er, I mean software upgrades... ;-)

Development environments.  I'm doing home automation right now, but I realize
that I want to change the program as I go.  I don't want to uninstall and
reprogram my lightswitches everytime I change the program, so I make my bootload
operate with a basic network protocol.  When the next big thing comes along
(CAN, LON, etc) (as long as I plan my hardware ahead of time) I can reprogram
all of my nodes to use and interface with the new protocol.

-Adam

Alice Campbell wrote:
> what is the rom loader discussion about?
> whats a rom loader?
> sorry for my ignorance, but its probably reversible.
>
> alice