Erratic Trace Measurements - HP 1660CS-Series User Manual

Preprocessor Problems

Erratic trace measurements

Erratic trace measurements
There are several general problems that can cause erratic variations in trace
lists and inverse assembly failures.
Ensure that the preprocessor configuration switches are correctly set
for the measurement you are trying to make.
Some preprocessors include configuration switches for various features (for
example, to allow dequeueing of the trace list). See your Preprocessor User's
Guide for more information.
Try doing a full reset of the target system before beginning the
measurement.
Some preprocessor designs require a full reset to ensure correct
configuration.
Ensure that your target system meets the timing requirements of the
processor with the preprocessor probe installed.
See "Capacitive Loading" in this chapter. While preprocessor loading is slight,
pin protectors, extenders, and adapters may increase it to unacceptable
levels. If the target system design has poor timing margins, such loading may
cause incorrect processor functioning, giving erratic trace results.
Ensure that you have sufficient cooling for the preprocessor probe.
Current processors such as the i486, Pentium™, and MC68040 generate
substantial heat. This is exacerbated by the active circuitry on the
preprocessor board. You should ensure that you have ambient temperature
conditions and airflow that meet or exceed the requirements of the
microprocessor manufacturer.
10–7