Intel MCS48 User Manual page 369

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.
"*
*
FjJQsta
status
ition
In
a
Sensor Matrix
mode,
a
bit
is
s^*i%tn^
word
to
indicate that
at
least
one
sensor^au/
A
is
contained
in
the
Sensor
RAM.
In
Special Error
Mode
the
S/E
bit is
showing
the|.e«pr*fl^jjy|
and
serves as
an indication
to
whether
a
simutfaj^usfj
multiple closure error
has occurred.
%^
FIFO
STATUS
WORD
x FIFO
Full
a h
ii
s/i:
T
_
Number
of
characters
in
FIFO
Error-Underrun
Error-Overrun
Sensor Closure/Error Flag for
Multiple Closures
Display unavailable
APPLICATIONS
8-BIT
MICRO
DATA
PROCESSOR BUS
SYSTEM
UAIM
DUO
{
ADDRESS/
BUS\
CS
KEYBOARD
-J
MATRIX
%.
RETURN
LINES
8
COLUMNS
8
ROWS
7T
SHIFT
CNTL
R„_
7
INT
\>
5V
1
IOR
iovv
RESET
CS
A0
CLK
3
-
8
DECODER
~r
7\,
4
-
16
DECODER
BLANK
DISPLAY
KY
I
Z3
?=>
iz
ADDRESSES
(DECODED)
DISPLAY
CHARACTERS
DATA
*Do not
drive
the keyboard decoder with the
MSB
of the scan
lines.
8-79
00742A