Setting up my trusty ol' Tait programmer f/ICSP, and think I
have it figured all out (from the Microchip docs), but running
this past the list to see if anyone might notice any potential
snags or things I may have missed.
Here are the necessary gory details:
(A) Initial circuit...
- 5V power.
- RC oscillator.
- RB6 and RB7 unused
- MCLR to +5V directly.
[All coded and working.]
(B) Modifications f/ICSP...
- MCLR to +5V via diode (using 1N4001 which I had)
- X'tal & ext caps, though possibly 3-pin resonator later.
(Avoiding the 4 instructions at startup prob).
[Still working.]
(C) With ICSP...
- Added jumper from MCLR pin to Tait programmer.
- RB6 wired to Tait programmer.
- RB7 wired to Tait programmer.
- Ground on app circuit connected to Tait prog ground.
- App circuit will still be self-powered.
- Tait programmer will use its own power.
Trying to avoid frying yet another chip. Is it safe
to "flip the switch"???
Cheers,
-Neil.
-- http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
Lemme think about this...
- Prog MCLR floats, no problem.
- Prog MCLR goes to >12V, the diode blocks this from the
app-circuit Vdd.
- Prog MCLR goes to ground, the diode is now forward-biased
with the app-Vdd, and pretty much shorts to ground.
Ouch!
Good idea. I'll drop a few-K resistor in series with the
diode, so I now have:
App-Vdd -to- diode -to- resistor -to- MCLR.
> Lemme think about this...
> - Prog MCLR floats, no problem.
> - Prog MCLR goes to >12V, the diode blocks this from the
> app-circuit Vdd.
> - Prog MCLR goes to ground, the diode is now forward-biased
> with the app-Vdd, and pretty much shorts to ground.
> Ouch!
>
> Good idea. I'll drop a few-K resistor in series with the
> diode, so I now have:
> App-Vdd -to- diode -to- resistor -to- MCLR.
>
> Thanks much,
> -Neil.
>
>
>
>
Thinking of another option... shouldn't I be able to prevent
this condition by putting another diode in line with the >12V
MCLR signal coming from the Tait programmer?
Of course, I've been getting away with 11.8V instead of the
required 12V-14V, and this new diode would probably drop it
to an un-workable level, but I can work around that by making
a proper 13V-14V power supply.
Only reason I am considering this is that board-space is at
a major premium on this app, and every little 1/8-watt
resistor counts. The programmer can be ENIAC-sized, and
not matter to me.
part 1 2714 bytes content-type:text/plain; (decoded 7bit)
Sounds like the same thing, except that you have the R on the
other side of the diode. I've attached a pic for clarity. The
line with the X (below the R) will be cut.
Only thing I don't have is the cap, which I thought unnecessary.
It seems more for power-on-reset than for ICSP purposes, and I
don't see that as being necessary with the PIC's POR fuse set.
[ Correct me if I'm wrong here. ]
Cheers,
-Neil.
{Original Message removed} part 2 19076 bytes content-type:image/jpeg; (decode) part 3 154 bytes -- http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
Some of it is software specific, but the hardware considerations should
apply to
most programmers
I think it's under
Technical Information>In Circuit System Programming(ICSP)>ICSP and
Picall/P16Pro
Lyle Hazelwood
-- http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
Pic Dude wrote:
>
> Sounds like the same thing, except that you have the R on the
> other side of the diode. I've attached a pic for clarity. The
> line with the X (below the R) will be cut.
Just lose the diode and use a 10k resistor.
This *does* work fine. :o)
-Roman
AVN-TECH.COM>
