vcc/gnd

[steve ravet]

> 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