'WARNING:BATTERY-POWERED PIC USERS'
I've just found out from the Microchip rep here that I am partially the
reason for the programming alert on PIC16cXX devices. If you run the PIC
from battery power, read this completely.
About seven months ago, we ran into a batch of C54As that had an
incredible 100% defect rate. We ran extensive tests and found out that
the PICs were somehow out of spec concerning VCC (supposed to be OK up
to 6.25VDC). In fact, the equipment we have been making for over a year
has had no returns at all, and the original protos are still working
The defective chips worked fine at 5VDC, but if operated from anything
more than 5.9 volts (such as four fresh AAAs), they were dazed and
confused, sometimes aimlessly blinking leds, running in wierd loops,
etc. Amazingly, if powered up at 5V and then voltage was run up to 6.5V,
they worked perfectly! Weird.
The microchip factory support engineer explained that they actually
sawed the top off of samples that we sent them, and determined the
problem to be in the EPROM section. What was happening was that the
programming was only bringing the bits down partially, not completely.
That's why they worked at lower voltages...the bits were just low enough
to make the product work.
The new specs call for more hits to bring down the bit lower.
Interestingly, the new batch (now called PIC16C54B) does not have the
problem (or at least the samples I was given checked fine at 6.5V).
The problem is most noted with programmers that appear to program very
quickly, such as the Parallax. -Dave, EDS, Inc.
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