At 12:13 12/10/99 -0700, you wrote:
>At 02:14 PM 10/12/99 -0400, you wrote:
>>>chip has 2 Vdd pins and 2 Vss pins. Does it matter which ones I use? (My
>>
>>Yes, it matters, and the answer is BOTH!
>>
>>Andy
>>
>
>I'm planning on implementing this feature on a 16F876.  I was hoping to use
>the LVP mode so as to get by with only three connections.  Has anyone on
>the list actually implemented this successfully?  I will try it as soon as
>time permits with my parallax programmer, but I'm not sure it supports this
>mode.  It seems to me if I jumper the PGC and PGD pins to the proper pins
>of my programmer and give it 5 volts it should work.
>
>Thanks in advance.
>
>-Erik Reikes

The parallax programmer unfortunately sources the VDD though a single I/O pin
of the PIC firmware chip. There is no transistor/FET buffering and if you
look at the programming specs you will see that this condition is way out of
spec. Personally, I could not trust the parallax programmer to reliably
program (I.E. over time) the flash parts however you can always power the
target circuit to supply the 5V (as it seems you are planning) and get around
this problem.

More important to note is that if the LVP pin is raised simultaneously with
VDD, the flash parts lock-up and you cannot enter the program mode. There
must
be a delay before raising LVP. This can be done with a simple RC network
as done on the PROPIC II programmer.

If you are powering the DUT from the target board then I would think that
connecting the programmer's switched VDD to the LVP would work and solve both
problems together.








Regards,

Jim Robertson
NEWFOUND ELECTRONICS
________________________________________
Email: newfound@pipeline.com.au
http://www.new-elect.com
MPLAB compatible PIC programmers.
________________________________________