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8279, 8279-5
Entry appears
to
be
from
the initial
entry
point.
8/16
Character
Display Formats
If the display mode is set
to
an 8 character display, the on
duty-cycle
is
double
what
it
would
be
for
a 16 character
display (e.g.,
5.1
ms scan time
for
8 characters
vs.
10.3 ms
for
16 characters with 100 kHz internal frequency).
G.
FIFO Status
FIFO
status is used in the Keyboard and Strobed Input
modes
to
indicate the
number
of characters in the FIFO
and
to
indicate whether
an
error has occurred. There are
two
types
of
errors possible: overrun and underrun.
Overrun
occurs
when
the
entry
of
another character
into
a
full
FIFO is attempted. Underrun occurs when the CPU
tries
to
read an
empty
FIFO.
The FIFO status word also has a
bit
to
indicate that the
Display RAM was unavailable because a Clear Display
or
Clear All
command
had not completed its clearing
operation.
APPLICATIONS
INT
SHIFT CNTL
INT
8-81T
DATA
BUS
MICRO-
DATA
~
DO_7
PROCESSOR
BUS
SYSTEM
CONTROLS {
iijj
lOR
WR
8279
lOW
RESET
RESET
CS
CS
ADDRESS
{
BUS
c/o
c/o
ClK
In a Sensor
Matrix
mode, a
bit
is set in
the
FIFO status
word
to
indicate
that
at
least
one
sensor
closure
indication
is contained
in
the Sensor RAM.
In Special
Error
Mode the
S/E
bit
is
showing
the
error
flag
and serves as an
indication
to
whether
a simultaneous
multiple
closure
error
has occurred.
FIFO STATUS
WORD
,FIFO
Full
Flag
for
SHIFT
KEVBOARD
MATRIX
CONTROL
8/
8 COLUMNS
RETURN
LINES
8 ROWS
'>-
8
"0_7
3
voo
3-8
DECODER
v
..
Jv
~
3lsa
8
0
_
3
4/
SCAN
LINES
(:'
4--16
DECODER
CLOCK
CLK
SO
_
3
A
O
_
3
BD
BLANK
r;6
I
~'~lAY
4
ADDRESSES
(DECODED)
DISPLAY
4
CHARACTERS
/
DATA
DISPLAY
FIGURE
2.
GENERAL
BLOCK
DIAGRAM
9-77
AFN-00742A-08