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[DPRG] Programming PICs at 3.3V through ICSP
Subject: [DPRG] Programming PICs at 3.3V through ICSP
From: Jeff Sampson
jsampson at pobox.com
Date: Wed Apr 23 00:14:29 CDT 2008
Hi,
Is anybody using PIC processors? I have a need to program 2 types of
PICs with a VDD of 3.3V. I can't raise the VDD to 5V like Microchip
wants me to do.
This has to be done through the ICSP interface with our own custom
circuitry. I.e., I'm not looking to use an external programmer.
(Or at least about $50k worth of boards thing I should be able to pull
this off. ;-)
Their data sheets sort of hint that it can be done, but all of their
examples show using the 5V bulk erase.
The two parts in question are the 16F917 and the 16F886. They are both
new enough to have row erase commands and I am able to erase program
space at 3.3V. I can't seem to erase config space at 3.3V, mainly
because I can't figure out from their data sheet how to do it. Or is
config space really considered program space? Again I can't determine
that from their data sheet.
(Another confusing factor is that bulk erase appears to work on program,
config and EEPROM at 3.3V, even though they say it will not work at
lower than 4.5V.)
I did have an inspiration while I was doing another futile Google search
tonight. The ICD-2 programmer does apparently program the chips. And the
VDD on the board is at 3.3V. I checked with a scope and it is not
raising VDD to 5V. So they may be using the elusive command sequence
that I am looking for, or they are using bulk erase and it just happens
to work.
So... I am going to connect my scope tomorrow and count bits to see what
commands they are sending. But if someone happens to know the trick, it
will save me a lot of bit counting. :-)
--
Jeff Sampson
http://tcrobots.org/members/jsamp.htm
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