•
Portable
PLUS
Computer
Reference
Information
10·7
10.3
Descriptions
of
Diagnostic Tests
The
following
paragraphs
summarize
the
operation
of
the
built-in, disc-based,
and
EPROM diagnostic
tests. This information
may
be
useful for interpreting test results.
In
order
for
the
test program to
run
and
display its menu, certain functions
of
the
computer
must
operate, either partially
or
entirely. These functions include:
• Display.
• Display controller.
• Display RAM.
• Latches, buffers,
and
decoders for
the
CPU
circuit, display circuit,
and
address/control
circuit.
• Clock circuit.
• PPU.
• Power
supply.
• Configuration EPROM.
•
Keyboard (key
not
stuck).
•
Certain
ROM ICs (several for disc-based test; hightst two for built-in
and
EPRPM tests).
• Multi-controller (for disc-based test).
The
built-in test checks
part
of
the
CPU
and
display RAM during its
startup
routine.
1
0.3.1
System
Test
The
System test includes all
of
the
tests described below except for the SLEEP test.
10.3.2
CPU Test
The
CPU
test checks
about
90 percent
of
the CPU functionality, including tests
of
its registers,
ad-
dressing,
and
stack operations.
10.3.3
ROM Test
The
ROM test computes the checksum for each system ROM
Ie
(plus
the
configuration EPROM)
by
stepping through
the
address space sequentially; then
it
compares the value with
the
proper
value
stored
in
the
configuration EPROM. The test further computers the checksum for each system ROM
IC
by
cycling through
the
address space in 16-byte steps;
then
it compares
the
value with the
proper
value from the configuration EPROM.
10.3.4
RAM Test
The
EPROM-
based
RAM test clears memory;
the
disc-based
RAM
test preserves memory. This test
checks system RAM
and
mass storage RAM,
but
it
doesn't
check
the
display
RAM.
The
RAM test checks
the
RAM
select circuit, RAM address latches,
and
transceivers
by
sending
one
byte to each of
the
RAM ICs, then reading those bytes back from all
res.
It
repeats this cycle starting
at each RAM
Ie.
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