Intel MCS48 User Manual page 358

8278
Data Format
In
the scanned keyboard mode,
the code
entered
into
the
FIFO
corresponds
to
the position or address
of
the switch
in
the
keyboard. The
MSB
is
relevant
only
for special
function keys
in
which code
"0" signifies
closure
and
"1"
signifies release.
The
next four
bits
are the
column count
which
indicates
which column
the
key
was
found
in.
The
last
three
bits
are from
the
row
counter.
KEY CODING
SF
M
6
1
FOR
SPECIAL FUNCTION
-MODE AND
KEY RELEASED
0FOR
KEY DEPRESSED
Display
Display data
is
entered
into a 16x4 display
register
and
may
be entered from
the
left,
from
the
right or into specific
locations
in
the display
register.
A new
data character
is
put out
on
B0-B3 each time
the
M6-M3
lines
change
(i.e.,
once
every 0.75ms
with a 6
MHz
crystal).
Data
is
blanked
during the time
the
column
select
lines
change by
raising
the display outputs. Output
data
is
positive true.
Left Entry
The
left
entry
mode
is
the simplest display format
in
that
each
display position
in
the display corresponds
to
a byte
(or nibble) in
the Display
RAM.
Address
in
the
RAM
is
the
left-most display
character
and
address 15
is
the
right-
most
display character. Entering characters
from
position
zero causes
the display
to
fill
from
the
left.
The
17th
character
is
entered back
in
the left-most position
and
filling
again
proceeds from
there.
Right Entry
Right entry
is
the
method
used by most
electronic
calculators.
The
first
entry
is
placed
in
the right-most
display character.
The
next entry
is
also placed
in
the
right-most character
after
the display
is
shifted
left
one
character.
The
left-most
character
is
shifted
off
the
end
and
is lost.
DISPLAY
RAM
ADDRESS
1
2 14 15
0*
1ST
ENTRY
1
2
3 15
1
2ND
ENTRY
1
2
3 4
1
2
3RD ENTRY
1
2
3
1
13 14 15
16TH
ENTRY
1
2 14 15 16
1
2
14 15
17TH
ENTRY
2 3 15
16
17
2 3 15
1
18TH ENTRY
3
4
16 17 18
Note
that
now
the display position and
register
address do
not correspond. Consequently,
entering a character
to
an
arbitrary position
in
the
Auto Increment
mode may
have
unexpected
results.
Entry
starting at
Display
RAM
address
with sequential entry
is
recommended.
A
Clear Display
command
should be given before display data
is
entered
if
the
number
of
data characters
is
not equal to
16
(or 8) in
this
mode.
DISPLAY
CHARACTER
~\
/ \ /
\
/
\
/
\
/
\
/
V
Figure
5.
Display Timing
8-68
00227A