QUICK-AND-DIRTY 16F84 PROGRAMMER
                     ================================

                               David Tait
               
                   
                         
If you have a source of +12V-14V and +5V available you can program 16F84s 
with virtually no hardware.  The schematic in qandd.pcx shows one possible
setup.  This is more or less the simplest circuit possible.  In one design
I've seen (Mark Cox's BLOWPIC) things are made even more simple by 
connecting the PIC directly to the parallel port but the 1k resistors add a 
little protection (the values are not critical but don't use less than 1k).  
Adding a few more components will make things a lot more convenient (see
topic02.zip in my PIC archive for a more elaborate version; or, if
I ever find time to document it, my hardware for programming 16F84s 
in-circuit via the PC serial port).  The quick-and-dirty circuit has several 
limitations and one very big plus point: it should only take a few minutes 
to lash the thing together.  The hardware is usable with the pp V-0.5 
software described in pp.txt and program.txt but, because there is no way of 
reading the PIC, pp must be run with the -n switch and the PIC can't be 
dumped or verified.  One other drawback with this setup is that program 
memory and data memory can't be programmed together.  Using a hex file with 
both program and data memory specified will only give correct results
for program memory.  If this is a problem the hex utilities in pichex01.zip
(from my PIC archive) can be used to split the hex file so that each area 
can be programmed separately.  As most PIC applications don't really need 
the data memory to be programmed it's not likely to be a major limitation 
in practice.  


Although they were simply meant as examples of how to customise pp the 
files mypp.bat and mypp.pif are in fact ready to use with the hardware 
described in qandd.pcx.  To use the quick-and-dirty programmer: insert a 
PIC (any of the 16x8x family); then, making sure the switch is closed, turn 
on the power supplies; run mypp with a command line of the form:

     mypp [ -xyz ] prog.hex
     
where -xyz is an optional set of valid pp switches excluding -! or -s
and prog.hex is the name of the hex file to be downloaded (using 
mypp rather than pp itself ensures that the software uses the correct setup, 
i.e. ppsetup=3, and that the -n switch is specified);  when pp asks you to
"Insert PIC ..." open the switch and hit any key (or control-C to abort); 
when pp exits close the switch, turn off the supplies and remove the PIC.
You can run mypp from a Windows DOS box or drag mypp.pif onto a Windows 
folder for lazy "double-click" execution (you'll need to use the Windows PIF 
editor to set the appropriate command line though).


If you add another single-pole double-throw switch wired so that it selects
whether the /MCLR resistor is connected to +12V-14V (as shown) or to +5V 
you get a crude form of in-circuit programmer.  This is roughly speaking how 
Derren Crome's Everyday Practical Electronics setup works.  When the new 
switch is in the +5V position the existing switch either resets the PIC 
(closed position) or lets it run (open position).  Of course, for the PIC to 
do anything useful you'll need to add oscillator components and make 
connections to some of the remaining port pins (as RB6 and RB7 are used for 
programming they are unavailable).  You could try this out using the relevant 
bits of the setup shown in test.pcx.  To program/reprogram the PIC you should 
first close the reset switch and select the +12V-14V supply with the other
switch; then run mypp with whatever else you need on the command line 
(mypp walk.hex for example); when pp asks you to "Insert PIC ..." open the 
reset switch and hit a key; when pp exits close the reset switch and reselect 
the +5V supply; finally, open the reset switch at which point the PIC should 
start running.  Sounds complicated but you'll soon get the hang of it:
reset closed - select +12V-14V - reset open - reset closed - select +5V -
reset open.  (Adding a couple of transistors as described in topic02.zip
automates these steps.)  Build everything on a solderless breadboard and 
you don't really need the switches at all as you can get the same effect 
by moving a couple of wires about.

If you don't have power supplies available you'll need a few more components
to get you going.  There are several options: one that I hesitate to mention
is to steal the supplies from your PC via a spare floppy disk power connector
- do this at your own risk (and the risk is considerable!); use a regulated
12V supply (12V battery or 8 AA batteries or whatever) and a 7805 regulator 
plus a couple of decoupling capacitors to get +5V; use the power supply parts 
of the programmer shown in pp.pcx together with an inexpensive "battery 
eliminator" on its 12V setting (which will typically produce about 16V-17V 
so don't be tempted to omit the 78L12 regulator); use a regulated +5V supply 
plus a couple of small 9V (PP3) batteries in series instead of the +12V-14V 
supply and connect a 12V zener diode from /MCLR to ground; use a regulated 
+5V supply and a DC-DC converter (one of the 8-pin Maxim chips for example) 
to get +12V; you get the idea ...


Have fun.


V-0.3 20 April 1998