Tandy 2000 Service Manual page 221

Tandy@
Model
2000
Service
t.Ianual
ADDRESS
RANGE
Write Input
Row
Address Select
WORD SEGMENT
Column
Address Select
Data Input Parity
Data Output
Parity
8-bit
Memory
Address
Bus
15-bit
Memory
Data
Bus
OOOOOH-lFFFFH 2OOOOH-3FFFFH
WRO
*
RASO*
UPPER
CASL*
DI PL
DOPL
WRI
*
RAS
I*
LOIIIER
CASU*
DI
PU
DOPU
DIVIEI,IAO
O
-DMEMAO
7
IBO O-
IB15
7
.5.4
Troubleshooting
Memory Read
or Write errors
can be
deLermined
by using
the
memory
diagnostic routines that are available for the
lt'lodel
2000.
After initiali
zLng
the test
program'
a top of
memory
algorithm is
executed
to
deLermine how much memory
has
been
installed in the
Itlodel 2000 under
test. If the
response
to
the
memory
size inquiry
does
not
agree
with the
amount
of
memory
the user
has
installed, it
can be
assummed
that
either the
memory
installation
was
not
performed
correctly
or the
memory
boards
installed are defective.
The user
should check
all
connectors
to insure proper
and complete
mating
before attempting to isolate a defective board
and/or
component.
Once
the user is confident of the installation integrity,
the
memory
diagnostic test
may
be
run.
There
are
three
tests that are available: a
read/wrLLe
data test; a
long
modified
address
test
and
a short modified
address
test.
The
data test writes a
known
data pattern to all
memory
locations.
The
data is
then read back
and
compared
to
the
known
data pattern for errors. Errors
generated
by this
test
would
indicate a
problem
either
on
the
data,/address
bus
interface to
memory
or with the
decoders
associated
with
the
memory
array.
2L2
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