Intel MCS48 User Manual page 364

8279/8279-5
FUNCTIONAL
DESCRIPTION
Since data input and
display are an
integral part of
many
microprocessor
designs, the system designer needs an
interface that can
control these functions without placing
a large load
on
the
CPU. The
8279 provides
this
function
for 8-bit microprocessors.
The 8279
has two
sections:
keyboard and
display.
The
keyboard
section
can
interface to regular typewriter style
keyboards
or
random
toggle
or
thumb
switches.
The
display section drives alphanumeric
displays or a
bank
of
indicator
lights.
Thus
the
CPU
is
relieved
from scanning
the
keyboard
or refreshing the display.
The
8279
is
designed
to directly
connect
to
the
microprocessor
bus.
The
CPU
can program
all
operating
modes
for the 8279.
These modes
include:
Input
Modes
•
Scanned
Keyboard
—
with
encoded
(8x8
key
keyboard)
or
decoded (4x8
key keyboard) scan
lines.
A
key depression generates a
6-bit
encoding
of
key
position. Position
and
shift
and
control status are
stored
in
the FIFO.
Keys
are automatically
debounced
with 2-key lockout or N-key
rollover.
Scanned
Sensor Matrix
—
with
encoded
(8x8
matrix
switches) or
decoded (4x8
matrix switches) scan
tines.
Key
status
(open or closed) stored
in
RAM
addressable
by
CPU.
Strobed
Input
—
Data
on
return lines
during control
line
strobe
is
transferred to FIFO.
Output
Modes
• 8 or 16 character multiplexed displays
that
can be
or-
ganized as dual
4-bit or single
8-bit
(Bq= D
,
A3=
D7).
• Right entry or
left
entry display formats.
Other
features
of
the
8279
include:
•
Mode programming
from
the
CPU.
•
Clock
Prescaler
•
Interrupt output
to signal
CPU
when
there
is
keyboard
or
sensor
data available.
•
An
8 byte FIFO
to store
keyboard
information.
• 16 byte
internal
Display
RAM
for
display
refresh.
This
RAM
can
also
be read by
the
CPU.
CLK RESET
c
DATA
BUFFERS
CS A
I/O
CONTROL
FIFO/SENSOR
RAM
STATUS
INTERNAL
-
DATA BUS
(8)
iz
DISPLAY
ADDRESS
REGISTERS
^
16x8
DISPLAY
RAM
lz
CONTROL AND
TIMING
REGISTERS
FIFO/SENSOR
RAM
KEYBOARD
DEBOUNCE
AND
CONTROL
iz
DISPLAY
REGISTERS
TIMING
AND
CONTROL
\7
7\
SCAN COUNTER
T\
OUT A
03
OUT
B0.3
\7
SHIFT
RL
7
CNTL/STB
8-74
00742A