49
4.3.1 Signal system for
the
8255 block
The
8255 (Programmable peripheral interface) is responsible for control
of
the
automatic cassette
deck, reverse operation
of
the
CRT display, blank control, memory switching between
the
IPL and
normal states, control
of
source pulse
output
for sound generation and control
of
keyboard LEDs.
FIGURE 4.8 summarizes the signal system for the 8255.
Keyboard
RVS
LED
GRPH
SFT
LOCK
8255
PA
7
Cassette
deck
control
PA
6
PA,
D7
8
PA
4
I
STOP
PA
3
Do
PLAY
PA
2
FF.
REW ready
PA,
MOTOR ON
PA
0
A,
Write
data
PC
7
Ao
RD/WR
PC
6
FF
. REW
latch
PC
5
-
EJECT
PC
4
RD
PC
3
- -
WR
PC
2
Read
data
PC,
RESET
Set ready
t---
PC
0
-
Pawl
provided/not
r--
cs
provided
.-------
PB
7
PB
6
PB
5
Display
/sound
control
PB
4
__.,
PB
3
--10
PB
2
REVERSE
--10
PB,
Required-BLANK
I
PB
0
V-BLANK
+5V GND
SOUND
GATE
SEL MEMORY [
BOOT/NORMAL
PIO B
7
FIGURE 4.8 Signal system for the 8255 block
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