Table of Contents
Advertisement
INTERRUPTS TEST
A4U51
When an interrupt condition occurs, it is latched into A4U51, A code corresponding to the highest priority active inter¬
rupt appears at the output of A4U52, which is connected to the interrupt inputs of the microprocessor (A4U27).
If a seif test interrupt error occurs, check the lines entering A4U51. If a higher priority interrupt is stuck on, no lower
priority interrupt can occur; therefore, the real problem may not be the one indicated by the self test. When self test
stops on an interrupt error, the error state should continue to exist, so it can be examined. If the inputs to A4U51
are as expected according to the chart below, check A4U51, A4U52, and A4U27 (low probability that microprocessor
A4U27 failure would lead user to this area).
Type of Interrupt
INTERRUPT INPUTS
INTERRUPT OUTPUTS
U51-13
U52 t
U51-11
U51-6
U51-3
U52-6 INTJf
U52-7 INTI
U52-9 INT2
(Highest Priority) P0N2
L
X
X
X
X
L
l
L
Sig. Anal.
H
t
X
X
X
L
H
H
Pwr. Mesh
H
H
L
X
X
H
L
L
HP-18
H
H
H
L
X
!
n
L
H
Timer
H
H
H
H
l
iui
H
L
None
H
H
H
H
H
H
H
H
If an input to A4U51 is wrong, trace the signal back to its originating circuit using the following guidelines.
Figure 5-31.
Self Test Failures
(Sheet 1 of 3)
5-44
Advertisement
Table of Contents
