Intel MCS48 User Manual page 71

EXPANDED
MCS-48
SYSTEM
PROGRAM MEMORY
>
ADDRESS
2708/
cs
2308
DATA
OUT
DECODER
°
1
10F4
2
E
3
*-
PORT
^,3
ALE
8048
BUS
PSEN
4
^
2
O
8212
LATCH
\S
ADDRESS
<*
2
o
7
Z
2308
DATA
OUT
10 >
<v
1
—
V
1
|8
ADDRESS
CS
2708/
2308
DATA
OUT
>
Is
EXPANDING MCS-48™
PROGRAM MEMORY
USING
STANDARD
MEMORY PRODUCTS
Also
shown
is
the
addition of
2K
words
of
program
memory
using an 231
6A
2K
x 8
ROM
to
give
a
total of
3K
words
of
program
memory.
In
this
case
n
o
chip select
decoding
is
required
and
PSEN
enables
the
memory
directly
through the chip select
input.
If
the
system requires only
2K
of
program
the
same
configuration
can be used
with
an
8035
substituted
for
the 8048.
The
8049 would
provide
4K
with the
same
configuration.
The
next
figure
shows
how
the
new
8755/8355
EPROM/ROM
with I/O interfaces directly to
the
8048
without the
need
for
an address
latch.
The
8755/8355
contains
an
internal 8-bit
address
latch
eliminating the
need
for
an
8212
latch.
In
addition
to
a
2K X
8 program
memory
the
8755/8355
also contains 16
I/O
lines
addressable as two
8-bit ports.
These
ports are
addressed as
external
RAM;
there-
8048
BUS
PSEN
8212
LATCH
Iz
c>
ADDRESS
2316
ROM
DATA
OUT
CS
USING
2K
x 8
ROM
EXPANDING MCS-48™
PROGRAM MEMORY
USING
STANDARD
MEMORY
PRODUCTS
3-3