On Sun, 14 Dec 1997, Mike wrote:

> I hope to find a simple answer, but not sure if there is one to this question.
> Whats the difference in the various PIC programmers I see on various links?

Implementation.  Programming a C84 is about as simple an interface as
 it can get.  It uses the clock provided by the programmer to clock
 data in and out, it uses 5/0v levels (except for /MCLR), etc.

I imagine that embedded 'programmers' just provide a buffer from the host
 to target PIC, and a easy means to switch /mclr.   Unless it had alot
 of ram I doubt it would buffer the target object code at all.

> I have noticed alot of 16C84, or F84, programmers and the hardware is
> straight forward.  Parallax's 16Cxx programmer has a firmware chip but no
> extra hardware on their PCB.  I have the parts to build a simple 16C84
> programmer that I wanted to use for some 16F84's I just got but not sure if
> the programmer I was going to build will work for the 16F84, since there
> seems to be some issue of it can only program the 16C84--I thought the chips
> were (C84 and F84) about the same.

There are minor programming and memory differences between them, but they
 are both still byte eraseable and programmable by the same hardware w/
 just a small change in the algorythm.

> Question #1:  Can I use a simple 16C84 programmer ( the one I had intended
> on building is called the "COM84") to program 16F84's?

With software that specifically lists 16F84.   The programmer itself shouldnt
 require any change unless the programming algorythm is entirely in firmware.

> Question #2:  Whats special about these programmers I see for all of the
> other 16Cxx chips--is it firmware or what?  If I use Parallax's SPEP.exe
> software to program, lets say a 16C56 or 57, and use the simple programmer I
> wanted to build for the 16C84, would this work or kill the 16C56 or 57?

There is some shareware for the parallel port programmers that program
 pretty much all the 16x devices and some do the 12x devices..  Using
 a 'dumb' programmer may be better since new devices can be implemented
 in software w/ just an extra socket and wiring the lines to the correct
 pins.

> Qestion #3:  Whats the alternative if a simple programmer ( such as the one
> for 16C84's) won't work for other 16Cxx chips short of buying a commercially
> made programmer such as Parallax's?  Are there any homebrew programmers out
> there for the 16Cxx series PIC chips that can be built from scratch?

After much screwing around figuring out how the ports worked, I created
 a quick-n-dirty 16x84 programmer for my needhams pb10 eprom blower. (BTW: a
 big no-thanks to needhams for refusing to support devices the programmer
 is easily capable of programming)

I suggest if you have the time that you build your own, and if you have
 even more time, write the software. You will learn alot about the hardware
 (both PC and PIC) doing it.  At least I did. :)

If you only build a parallel port type programmer, there are some nice
 shareware/freeware programming programs that can be had for a song.

Steve

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