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a) Signals around
the
8255
The 8255 Programmable Peripehral I/O Controller assumes
the control
of
the cassette recorder, CRT screen cursor
Port
PA
($EOOO)
PB
($EOOl)
PC·
($EOO2)
Cassette
control
Key data
input
terminal
(8P)
RDATA
MOTOR
M·ON
WDATA
Key data
strobe terminal
(lOP)
Port terminal
PA
o
PAl
PA
2
PA
3
PA
7
PB
o
PB
I
PB
2
PB
3
PB
4
PB
s
PB
6
PB
7
PC
I
PC
2
PC
3
PC
4
PC
s
PC
6
PC
7
r---
'-
VBLNK
5560UT
INTMSK
556RST
0
LS
0
\
145
-
C
B
9
A
I/O
Active state
H
OUT
H
L
L
IN
L
OUT
-
OUT
L
OUT
51..
IN
H
IN
-
IN
-
IN
-
blinking timing, keyboard scan strobe output, and key
return data.
8255
PBO
\
0,
PB7
\
Do
PC7
PC6
AI
PC2
PC5
Ao
PC4
PC3
RD
PCl WR
CS
PA7
RESET
PA,
PA.
PAl
PA
o
Control function
}
Keyboud
scan stwhe slgnal output
Cursor blinking timer reset
Keyboard scan data input
Cassette data write
•
Timer interrupt disable
Motor rotate control
Motor rotation check
Cassette data read
Cursor blinking timer input
Vertical blanking
0,
AI
8255
RESET
Signal name
556RST
WDATA
INTMSK
M-ON
MOTOR
RDATA
5560UT
VBLNK
•
Output
data handled in the
bit
cell mode. (Port C in control mode)
b)
Cassette controller
Data transfer with the cassette recorder is carried
out
on
PCI, PC4, and
PC5
of
the 8255. Shown next
is
the data
format (Sharp
PWM
method)
of
the cassette tape.
12