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".

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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'.