gnupic: PIC and TLVP programmer
Subject:
Re: PIC and TLVP programmer
From:
####@####.#### (Byron A Jeff)
Date:
1 Aug 2002 14:08:40 -0000
Message-Id: <200208011354.g71Dsne28916@cleon.cc.gatech.edu>
>
> Hi all,
>
> I would like to use Byron Jeff's TLVP programmer for programming PIC16F877 and
> PIC16F628. In datasheet of this chips is mentioned that if LVP mode is used
> the pins RB4 (F628) and RB3 (F877) can not be longer used as a general purpose
> IO pins.
That is correct.
>
> Does it means, if I use this programmer so those pins are reserved only for
> programming?
That is also correct. That pin must be grounded for general usage if LVP is on.
I've never been thrilled with the location of the pin. Ideally it should have
been at one end of a port or the other. However each and every other end port
pin on these parts have a secondary function that would be lost if reassigned.
With the 877's I generally don't mind too much as full ports C and D are
available. It's a bit tougher with the 628, but it's possible to recover
MCLR and one or both oscillator pins as general purpose inputs.
Finally I do have a high voltage programmer version that I designed but
I haven't had an opportunity to test yet. I've used similar designs in the
past so it should work. You can find the schematic here:
http://www.finitesite.com/d3jsys/proghvpv2.gif
Be aware that the Vpp pin is inverted in this design because you have to
ground the parallel port pin to get 13V and raise the pin high to get 0V.
So when you configure the software, you must indicate that the pin is
inverted.
After I get some testing in on the design I plan to post it to the main page.
Hope this helps,
BAJ
