827918279·5
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 int'erface 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
(8
x a key
keyboard)
or
decoded
(4
x a 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
FI
FO.
Keys are automatically debounced
with 2-key
lockout
or
N-key rollover.
elK
RESET
OUT
Ao.,
OUT
Bg.3
DBO-l
TIMING
AND
CONTROL
iii
• Scanned Sensor Matrix - with encoded (8 x a matrix
switches)
or
decoded
(4
x 8 matrix switches) scan lines.
Key status (open orclosed) stored in RAM addressable
by
CPU.
• Strobed Input - Data
on
return lines during control
line
strobe is transferred to'
FIFO.
Output Modes
• a
or
16
character multiplexed displays that can be or-
ganized as
dual 4·bit
or
single a-bit
(80
=
Do,
A3
= 07)'
• Right entry
or
left entry display formats.
Other features of the
8279
include:
•
Mode programming from the
CPU.
e Clock Prascaler
• 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.
SLO·3
IRa
KEVBOARD
DEBOUNCE
AND
CONTROL
RLO.7
CNTLISTB
9-72
AFN-OOl42A-OG
