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EXPANDED
MCS-48
SYSTEM
PROGRAM
MEMORY
J:
=4=======::;-;:=~DECODER
0,
r---...,
PORT
20·3
1
OF
4
27081
i----ICS
2308
1K·2K
ALE
1-----+1
8048
8212
LATCH
10
cs
27081
2308
2K·3K
PSEN~----------------------~
cs
27081
3K
·4K
2308
USING
lK
x 8
PROM/ROM
DATA
OUT
EXPANDING
MCS-48
™ PROGRAM MEMORY USING STANDARD MEMORY PRODUCTS
Also shown
is
the
addition of 2K words of
program memory using
an
2316A
2K
x 8
ROM
to
give a total
of
3K words of program
memory.
In
this case
no
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.
3
PORT
20·22
8048
ALE
8212
I?>
LATCH
A
BUS
B
PSEN
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-
"'
7
'"
11)
ADDRESS
2316
ROM
DATA
OUT
CS
USING
2K
x 8
ROM
EXPANDING MCS-48™ PROGRAM MEMORY USING STANDARD MEMORY PRODUCTS
3·3