Intel MCS48 User Manual page 221

8155/8156/8155-2/8156-2
DESCRIPTION
The
8155/8156 contains the following:
• 2k
Bit
Static
RAM
organized as 256 x 8
•
Two
8-bit
I/O ports
(
PA & PB
)
and one
6-bit I/O port
(
PC)
• 14-bit timer-counter
The IO/M (IO/Memory
Select) pin selects either the
five
registers
(Command,
Status,
PAo-7, PBo-7, PC0-5) or
the
memory
(RAM)
portion.
(See Figure
1.)
The
8-bit
address on
the
Address/Data
lines,
Chip
Enable
input
CE
or
CE, and IO/M
are
all
latched on-chip
at
the
falling
edge
of
ALE. (See Figure
2.)
7V
^L
L_.
8 BIT
INTERNAL DATA BUS
~~)
T>
Tt
f>
^
7>
77
i£^
^2
7\
/*
/'
/''
±L
77
^L
TIMER
MSB
it
TIMER
LSB
TIMER
MODE
V
V V
J
Figure
1.
8155/8156
Internal
Registers
CE"(8155)
\
/
/
\
OR
CE(8156) k
/
IO/M
\
/
\
\
^
A
°0-7
X
ADDRESS
y
DATA
VALID
^
^
/
ALE
\ /
RDORWR
\
/
NOTE:
FOR DETAILED TIMING INFORMATION, SEE FIGURE
12
AND
A.C.
CHARACTERISTICS
Figure
2.
8155/8156 On-Board
Memory
Read/Write Cycle
6-69