Where I went wrong
Mistake No. 1 Migration and Assumption are not good bedmates
Migration from the PIC16F77 to the PIC16F877A should be a walk in the park. I thought.
Where did I go wrong? The Configuration bits.
The 877A has an extra feature, that you dont see on the PIC16F77 (its hidden on MPLAB). The Low Voltage Program option bit,
if your application uses pin RB3 (pin 36 on the 40 pin dil), then you MUST set the low voltage program enable bit to OFF.
- Pin Compatible, Yes.
- Code Compatible, Yes.
- Speed Compatible, Yes.
- Straight drop-in, NO
If you don't do this, your application will appear to be stalled. The PIC is is program mode, you are chasing your own arse,
with a view to disappearing up it.
Obviously this only happens to you when you are
- Too lazy (in the first instance) to get the spec sheets out.
- Assuming (ASSUME, makes an ASS out of U and ME
Mistake No. 2 PP3 Batteries
(aka 6LR61, Transistor, E-Block, MN1604, The little square 9-Volt Job for Smoke alarms)
or The clue is in the title, as they say.
No matter how you look at a PP3 battery, (duracell in this instance), 9V is still more than 5V, well it was when I did maths,
you know, like "9 > 5" or in laymans terms, 9v Will fry your LCD display almost instantly.
Unfortunately, I didn't have any lay men nearby so I did just that. A nice solid block of black across the front which
very artisticly dispersed into a sort of grey fuzziness and then nothing. To paraphrase Monty Python, "If it hadn't been soldered to the
header strip, it would be pushing up daisies". Well OK, it is now. Gone, deceased, it is an ex-LCD.
The good that cam about from this destruction exercise, is that I got to take it apart and see exactly what the luminescent bit
is made of. - it looks like a strip of thin, pink plastic. How that one works is beyond me at this time, I have far too much
fun left in destroying my remaining PIC cpus and stuff.
Which, interestingly enough, brings me onto the next one...
Mistake No. 3 Untidy Workshop, and tangled wires.
My workshop is the spare bedroom in my house. It is much smaller than my last one, and smaller than the next (we are hoping to move house again soon and spare room is bigger :) )
I have my PC, twin LCD monitors, Cambridge Soundworks Amp. Epson 950 printer, Epson R300 Printer, ADSL Router, D-Link Wireless Lan Router, ISDN LanModem, iPAQ Charger, Second PC, Anglepoise Light, Soldering Iron, Warp-13 Charger (16v), Second PC (just to supply +5v to the PIC development board).
In fact the second PC is only there because mistake No. 2.5 (unlisted) was not my fault, but I had a 7805 +5v regulator that
decided to become a wire instead of a regulator. +16v in, +16v out, Goodbye PIC cpu, - This was the first casualty.
I dropped the +5v wire from the PC (hooked into a Hard Disk connector and out to a &Quot;normal&Quot; power connector.
I picked it up, plugged it in and zapped the PIC on the board. How? it's a very stable and clean +5V supply. No smoke, No crackles,
hmm, check the voltage, +16V ?
So why is that then? (It's those voices again)
The +5v cable was lying in precisely the position it had fallen a moment ago. But the +16V power cable for the Warp-13 programmer was no longer adorning the workshop floor. It was nicely slotted in place in the development board.
There must be a moral in this story somewhere, but suffice to say, the programmer plug is now Fixed into the programmer, and
the +5v clean lead is labelled VERY clearly.
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