IC Characterization - Conceptual DEMO

Beau Schwabe

I decided to post this because of this thread ...
http://forums.parallax.com/showthread.php?134303-Cannot-Detect-Propeller-on-a-Custom-made-Board

...an expanded 'Propeller' version of the idea below could be a fun project.

When I was a kid, maybe the age of 13, as an academic exercise, I made a 'chip identifier'
based on the concept illustrated below using several analog MUX IC's (The CD4067B was a favorite)
and an ATARI computer. Only I took it a step further and mapped out the analog response of several
possible combinations. The result was a way to accurately (with about 95% certainty) detect an IC,
and or detect a problematic IC that had previously been characterized. i.e. a damaged I/O etc.

This idea also lends itself to in-circuit characterization for a "known to be good" circuit. The power to the
circuit under test MUST be removed for proper characterization.

When probing 'another' Propeller IC, typical results:


Probe"A" and Probe"B" are both inputs              ... pseudo traingle wave
                                                       (typical capacitor charge/discharge)

Probe"A" is Vss and Probe "B" is an input          ... triangle wave with top clipping
                                                       at one internal diode drop.

Probe"A" is an input and Probe "B" is Vss          ... triangle wave with bottom clipping
                                                       at one internal diode drop.

Probe"A" is Vdd and Probe "B" is an input          ... triangle wave with bottom clipping
                                                       at one internal diode drop.

Probe"A" is an input and Probe "B" is Vdd          ... triangle wave with top clipping
                                                       at one internal diode drop.
                                                 
Probe"A" is Vss or Vdd and Probe "B" is Vss or Vdd ... flatline or attenuated triangle wave