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13.
7
PPI
(PROGRAMMABLE
PERIPHERAL
INTERFACE)
PPI
is
a
parallel
interface
IC equipped with
three
8-bit
input/output
ports
(PA, PB,
and
PC).
The
role
of each port
is
summarized
below.
PA
port
:
Generation of
slot
selector signal
PB
port:
Reading
of
key
inputs
from
the
keyboard
PC
port
:
Four
lower
bits
PCO
thru
PC3
:
Key
scanning
signal
generation
Four
higher
bits
PC6
:
CAPS
lamp
switching
PC4:
Cassette
I/F
remote
relay
control
PC5
:
Cassette data writing
PC7
:
Key
click
tone
source
Each
PPI
port
is
se lecte
d on
the b
asis
of
the
status
of
AO, Al,
WR,
and
RD
when
PP1=L and
CS=L
(see
Table
13-8).
The
formation
of address
images
is
prevented
by
using
A2
in
CS.
Note
that
the
MSX
is
used
in
mode
0.
Fig.
13-29
PPI
circuit
Table 13-8
Table 13-9
PPI
bit
allocation
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