HP 8924C Assembly page 543

Reading LED Codes
NOTE: The LEDs output Self-Test Diagnostic codes only when the Test Set is powering up. The
LEDs remain off when the Self-Test Diagnostic is initiated through programming or by
running the Miscellaneous Diagnostics. To read the LED codes, the Test Set's cover must be
removed.
N:\mkt\MANUALS\HP8924C\ALR\diagnos.fb
When the Self-Test Diagnostic reports a failure, more information about the
failure may be available inside the Test Set. This additional information is output
to the four LEDs on the top of the A16 Host Controller assembly. The failure
codes are layered, that is, sent out as code sequences.
Test Diagnostic Using the Internal LEDs," on page 544
document some of the more useful code sequences. You may need to run the Self-
Test Diagnostic several times to figure out a particular LED sequence.
If the Test Set has no faults that can be detected by the Self-Test Diagnostic, the
four LEDs on the Controller assembly will light and remain on for about ten
seconds. During that period, a short beep will be heard. Then the LEDs will
extinguish and remain off.
If a fault is detected during the test:
1. The four LEDs will go on for about four seconds.
2. The LEDs will blink a failure code which corresponds to the error listed in
"Returned Values for Self-Test Diagnostic Failures" on page 542 Figure 50, "First
LED Patterns," on page 545
3. Two non-blinking LED codes will follow. The interpretation of these codes depends on
the preceding blinking code. Two sets of the non-blinking codes are listed in
figure 51, "Non-blinking LED Codes For Serial Bus Communication Failure," on
page 546 and figure 52, "Non-Blinking LED Codes For Miscellaneous Hardware
Failure," on page 547.
4. If there is more than one failure, the test will loop back to step 2 and repeat until the last
failure is reported.
The pattern generated by the LEDs can be interpreted as a binary-weighting code.
The LED closest to the rear of the instrument (labeled "0") is the least-significant
bit. For example if the LEDs output the blinking pattern: Off, On, On, On (reading
front-to-back or LEDs "4 3 2 1"), the binary number is 0111 or decimal 7. The
error codes shown in
table 114 on page 542
weighted value for this example is decimal 2
example is easy to emulate; simply power-up the Test Set while holding a key
down.)
Chapter 14, Diagnostics Descriptions
Description Of Self-Test Diagnostic
shows the blinking LED codes.
are weighted by the binary value. The
7
= 128 or hexadecimal 80. (This
Figure 49, "Reading the Self-
and the tables following it
Table 114,
543