xpyttl wrote:
"Ken Scharf" wrote in message
...


diode from MCLR to VSS (Anode to VSS) and that brings the 'zero'
voltage down to -.37v or so.


You may want to check the datasheet for the specific part you are going to
use. the 16F628 datasheet, for example, specifies the absolute minimum
voltage on MCLR at -0.3v. Ditto with the 877 and 84A.

..


I could put a germainium or low voltage drop si in series with
the VPP to block the negative voltage all together. That would
somewhat limit the vpp, which might be a problem.

xpyttl wrote:
"Ken Scharf" wrote in message
...


diode from MCLR to VSS (Anode to VSS) and that brings the 'zero'
voltage down to -.37v or so.


You may want to check the datasheet for the specific part you are going to
use. the 16F628 datasheet, for example, specifies the absolute minimum
voltage on MCLR at -0.3v. Ditto with the 877 and 84A.

..


I added a diode in series with the VPP output from the emitter or Q1
(with the anode toward Q1's emitter) and a second shut diode
from the MCLR pin to VSS (anode toward VSS). Now the VPP voltage
at MCLR swings from -0.05v to +12.6 volts. I hope that's enough
VPP. I may have to change out the 8.2v zener, I measured the voltage
across it and it appears on the low side. I could also just connect
a 1n4001 or two in series with it to raise the vpp supply.

Anyway seems the programmer is safe now. Still need to put a scope
to the PGC and PGD lines and check they are in spec.

xpyttl wrote:
"Ken Scharf" wrote in message
...


diode from MCLR to VSS (Anode to VSS) and that brings the 'zero'
voltage down to -.37v or so.


You may want to check the datasheet for the specific part you are going to
use. the 16F628 datasheet, for example, specifies the absolute minimum
voltage on MCLR at -0.3v. Ditto with the 877 and 84A.

..


I added a diode in series with the VPP output from the emitter or Q1
(with the anode toward Q1's emitter) and a second shut diode
from the MCLR pin to VSS (anode toward VSS). Now the VPP voltage
at MCLR swings from -0.05v to +12.6 volts. I hope that's enough
VPP. I may have to change out the 8.2v zener, I measured the voltage
across it and it appears on the low side. I could also just connect
a 1n4001 or two in series with it to raise the vpp supply.

Anyway seems the programmer is safe now. Still need to put a scope
to the PGC and PGD lines and check they are in spec.

"Ken Scharf" wrote in message
. ..

I could put a germainium or low voltage drop si in series with
the VPP to block the negative voltage all together. That would
somewhat limit the vpp, which might be a problem.

I don't know definitively what you need here. A lot of older programmers
went through all sorts of hoops to be sure that value was above 12 volts.
However, lots and lots of folks have success with around 9 or so. I haven't
been able to find a spec, other than the maximum, but Microchip generally
refers to this as "13 volts".

...


...

"Ken Scharf" wrote in message
. ..

I could put a germainium or low voltage drop si in series with
the VPP to block the negative voltage all together. That would
somewhat limit the vpp, which might be a problem.

I don't know definitively what you need here. A lot of older programmers
went through all sorts of hoops to be sure that value was above 12 volts.
However, lots and lots of folks have success with around 9 or so. I haven't
been able to find a spec, other than the maximum, but Microchip generally
refers to this as "13 volts".

...


...

xpyttl wrote:
"Ken Scharf" wrote in message
. ..


I could put a germainium or low voltage drop si in series with
the VPP to block the negative voltage all together. That would
somewhat limit the vpp, which might be a problem.


I don't know definitively what you need here. A lot of older programmers
went through all sorts of hoops to be sure that value was above 12 volts.
However, lots and lots of folks have success with around 9 or so. I haven't
been able to find a spec, other than the maximum, but Microchip generally
refers to this as "13 volts".

..


..


I do remember reading that some pics failed to program if vpp wasn't
high enough. If 13v is the maximum than I must be close enough with
12.6v!

BTW My programmer has a 40 pin socket wired to accept 8,14 and 18 pin
pics in the bottom part of the socket (Device pin 1 9 pins up from the
bottom in all cases) and 28 pin pics in the upper part of the socket
(Device pin 1 at the top of the socket). I have a jumper to remove
vpp from pin 15, and one to set pin 12 at vss for 40 pin pics and
vdd for all others.
So in theory this unit will work with almost all pics.
For the 20 pin units I would need to put a socket into the
socket so pins 10 and 11 can 'hang ten'.

xpyttl wrote:
"Ken Scharf" wrote in message
. ..


I could put a germainium or low voltage drop si in series with
the VPP to block the negative voltage all together. That would
somewhat limit the vpp, which might be a problem.


I don't know definitively what you need here. A lot of older programmers
went through all sorts of hoops to be sure that value was above 12 volts.
However, lots and lots of folks have success with around 9 or so. I haven't
been able to find a spec, other than the maximum, but Microchip generally
refers to this as "13 volts".

..


..


I do remember reading that some pics failed to program if vpp wasn't
high enough. If 13v is the maximum than I must be close enough with
12.6v!

BTW My programmer has a 40 pin socket wired to accept 8,14 and 18 pin
pics in the bottom part of the socket (Device pin 1 9 pins up from the
bottom in all cases) and 28 pin pics in the upper part of the socket
(Device pin 1 at the top of the socket). I have a jumper to remove
vpp from pin 15, and one to set pin 12 at vss for 40 pin pics and
vdd for all others.
So in theory this unit will work with almost all pics.
For the 20 pin units I would need to put a socket into the
socket so pins 10 and 11 can 'hang ten'.

On Sun, 13 Jun 2004 21:45:46 -0400, "xpyttl"
wrote:

"Ken Scharf" wrote in message
...

I could put a germainium or low voltage drop si in series with
the VPP to block the negative voltage all together. That would
somewhat limit the vpp, which might be a problem.

I don't know definitively what you need here. A lot of older programmers
went through all sorts of hoops to be sure that value was above 12 volts.
However, lots and lots of folks have success with around 9 or so. I haven't
been able to find a spec, other than the maximum, but Microchip generally
refers to this as "13 volts".

Perhaps a visit to the PICLIST mailing list will be beneficial

On Sun, 13 Jun 2004 21:45:46 -0400, "xpyttl"
wrote:

"Ken Scharf" wrote in message
...

I could put a germainium or low voltage drop si in series with
the VPP to block the negative voltage all together. That would
somewhat limit the vpp, which might be a problem.

I don't know definitively what you need here. A lot of older programmers
went through all sorts of hoops to be sure that value was above 12 volts.
However, lots and lots of folks have success with around 9 or so. I haven't
been able to find a spec, other than the maximum, but Microchip generally
refers to this as "13 volts".

Perhaps a visit to the PICLIST mailing list will be beneficial

Ken Scharf wrote:

I'm going to use it on Linux with PikDev.
I use Jaakko Hyvatti's version of the JDM84
with picprog software. It works very well
on Linux.

http://www.iki.fi/hyvatti/

73, Ed. EI9GQ.



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