vcc and gnd

[Shannen Durphey]

Steve Ravet wrote:
> 
> ----------------------------------------------------------------------
> 
> Date: Sat, 17 Jul 1999 13:59:00 -0500
> From: steve ravet <Steve.Ravet at arm.com>
> Subject: vcc/gnd
> 
> > Date: Fri, 16 Jul 1999 20:35:28 -0400
> > From: Shannen Durphey <shannen at grolen.com>
> > Subject: Pretty Good Protection
> >
> > Hi, all.  I was attempting to copy a calibration last week, and was
> > having problems with the files coming up with zeros in all locations.
> > After several attempts, and much double and triplechecking various
> > items, I decided it was the memcal.  Some investigation, and handy
> > work with a pick and razor blade revealed that the programmer had
> > clipped pin 28 of the 27256 chip.  A small pin completed the open
> > circuit, but now I couldn't get a read that would verify.  More
> > investigation revealed another clipped pin, I believe # 14.  There's a
> > pinout here: http://www.twinight.org/chipdir/giicm/27256.txt
> > which shows the pins as VCC and GND.
> >
> > What is VCC
> > Am I remembering incorrectly about the GND pin being clipped? (they
> > were cross corner, top right and lower left of chip)
> > Is there a brief way to explain why this worked, and how the chip was
> > still able to work in the ecm?
> >
> > Shannen
> >
> 
> Vcc is power for normal chip operation.  Vpp is also power, but only
> used during programming.  That chip would not have worked in the circuit
> without vcc and gnd, maybe they got broken at some point?  Did you ever
> take it out of the socket?
> 
> - --steve
> 
> - --
> Steve Ravet
> steve.ravet at arm.com
> Advanced Risc Machines, Inc.
> www.arm.com
> 
You're not the first person to say it wouldn't work without power and
ground. LOL. Anyway, the pins were definitely clipped by the chip
tuner.  Was the pinout at the url in the original post correct?  I
could have the pin locations wrong, but I'm sure that they were on the
upper right and lower left of the chip, with the notch pointed up. 
Once I added some "jumpers" to replace the cut pins, I was able to
read the calibration.  Subsequent reprogramming of another chip with
that file worked fine, and the clipped chip worked perfectly when
re-installed.  Next time I'll take better notes.  
Shannen