JW wrote:
On Wed, 13 May 2009 07:51:38 -0400 Phil Hobbs
wrote in Message id:
:

JW wrote:
Let's say you know that a certain point on a data bus has a defective
device that is always trying to drive the bus low; Was wondering if anyone
has any good tricks in finding the defective device, other than
cutting/lifting pins?
Drive the bus high, e.g. with a 1k resistor to Vdd, and use
millivoltmeter. You can see the voltage drops in the traces--where the
voltage drop is changing, current is flowing.

Hi Phil, That sound like a good possibility, thanks. I have a Philips
PM2534 DMM that has a 300mV range with 100nV resolution. The only thing
might be that if the bus is active (changing states) the readings might be
jumping around too much. Often I see a tied node on a TTL bus that has
transitions from .5 to 2 volts or so. Any ideas for a situation like that?
Maybe try to crash the processor?

Yep. Hit the halt line. Alternatively, disable the clock. As a last
resort, you could put an RC filter on the meter.

Cheers

Phil Hobbs