S*TJ
MAY 1981
6
ANALYSIS
(PART 1)
by Jim Snead
General Manager
Electronics Division
Kurz-Kasch, Inc.
Dayton, Ohio
A means of isolating digital logic faults at the components level. Although considered
most useful in servicing micro-processor based products, the technique is applicable
to all digital systems. Basically, the technique involves the tracing of signals and the
conversion of lengthy bit streams into four-digit hexidecimal "signatures". Using
logic diagrams and schematics specially annotated with correct signatures at each
node and guided by troubleshooting trees, the technician traces back until he finds a
point in the circuit which has a correct input signature and incorrect output signature.
NODE
A point of convergence on a diagram, chart or graph. Nodes can be used to designate
a state, event, time convergence, or a coincidence of paths or flows.
16 ADDRESS BUS -.---~'-------.
CLOCK
CPU
ROM
RAM
1/0
8 DATA BUS
CONTROL
Here is a block diagram of a common bus oriented processor. The
clock is the heart of the system and is the timing for the entire processor.
A CPU accepts timing information horn the clock, generates addressing
information, control functions for various devices in the system, accept information
horn memory and/ or I. 0 . devices. This information or data tells the CPU what to do, it
does what it is instructed and generates a response to its instructions.
ROM is the permanent memory wherein resides the basic instructions for the
CPU. Without ROM the CPU can do nothing. (ROM here is defined as CPU
instructions).
RAM is the temporary storage medium where information is temporarily stored
until acted upon by the processor and moved to its final destination. RAMS also hold
partially processed data.
I. 0. (input-output) devices are the interfaces between the computer system and
the outside world.
Throughout the entire processor system, past each node, there are streams of
data. These data streams have two forms or characteristics which make them a
unique-quantity of "O's" and "l's" and the placement in time of them. Polarity of the
pulse is impo.rtant but its placement in time is equally important. The most practical
and most accurate method of determining if the time and polarity criteria is met is with
Signature Analysis.