National
MM2316 ROMs
The
National ROMs were
the
second
type
of
ROM
the
factory
received during
production.
These ROMs were used
in
a large
number
of
"0"
version Boards and
in
a few
"A
lf
version
Boards. These devices are
true
Read Only
Memories since
they
are
not
programmable (ex-
cept
by
the
vendor),
nor
are
they
eraseable.
They
may be identified by
the
colored ceramic
package (only a few)
or
in
24
pin dual-in-line
plastic packages.
The
ceramic packages have
the
part
number
MM2316 followed by
either
an
"R/D"
or
an
"5/0".
The
"R/D"
is
ROM
A and
the
"5/0"
is
ROM
B.
The
plastic packaged
ROM
has
the
part
number
"M2316E"
and
below
it
"MMS258ET"
followed by an
"R/N"
or
an
"SI-N". Once again,
the
"R/N"
is
ROM
A,
while
the
"S/N"
is
ROM
B.
These ROMs may be in
either
Z33
or
Z34
socket
and still
operate
correctly.
In
other
words,
ROM
A does
not
have
to
be in
socket
Z33. It
could
be
in
socket
Z34, and vice versa
for
ROM
B.
The
reason
you
need
to
know
the
differences
between
ROM
A and
ROM
B
is
in trouble-
shooting. Certain software
troubleshooting
aids
may
fail
ROM
A and pass
ROM
B.
You need
to
identify
ROM
A
to
replace it
or
for
further
troubleshooting.
*NOTE:
The
only differences between
the
Schematic on this page and
the
Master
Schematic
are
that
A
11
is
on Pin
20
and
ROM*
is
on Pin 18.
The
"D"
version Board with National ROMs will
usually have only
two
wire modifications
or
jumpers, directly
under
the
ROM
sockets. These
jumpers will also have
two
etch
cuts
associated
with
them.
Version
"A"
Boards using National
ROMs may have more jumpers. This
is
because
an
"A"
version Board may have been modified
to
use Intel EPROMs and
then
later remodified
to
accept
the
National ROMs.
Be
careful when
identifying
the
different
Board versions.
The
two
wire modifications associated with National
ROMs are shown in Figure 24. Notice
that
only
two
wires are switched around.
There
are no
spare gates used
in
this modification.
A
11
1>--
-.-
..::.20=_1
18
Z!33
18
ROM"
~34
FIGURE 24. National ROMs
in
Version
"D"
Board*
102
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