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Sharp MZ-800 Service Manual page 30

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MZ-800
Key strobe is issued through PAo-PAl to
~can
the key.
As it is supplied to the decoder, it makes one of outputs,
0-9, set low. It is then added to the key matrix to scan
the line of the key depressed (vertical key matrix scan).
The line is in the low state, if it is in depression
(horizontal key matrix scan).
NOTE: In the ready for command state, PAo-PAl are
normally repeats to be low state and the decod-
er outputs repeats to be high state. But, since
the decoder is of an open collector type, it
would not permit to check high and low state.
b) Cassette control
Decoder side
"H" Strobe signal
lJ
~ey
8255
switch
PB side
The 8255 issues the cassette write data from PC, and
Example
8255 output PA, PA
2
PA,
PAo
L
H
L
L
Only the LS145 decoder output 4 (#5
pin) is in low state.
Because the connector (5) is in low
state, key scan is permitted only for
keys, A through H.
State of the 8255 input port B.
PB
7
PB. PBs PB. PB, PB
2
PB, PB o
L
H
H
H
L
H
H
L
Above stata shows that keys, A, E, or
H, is in depression.
read signal through PC5. The type of data (input,
output) and its format are as follows:
___
~I
I I
. I'
SHORT
~
CASE 1
READ
EDGE
READ
POINT
LONG
LONG represents the bit value "'" and SHORT the bit
value "0". Data will be read at 368 microseconds after
(
SHORT
10 seconds
220CO
TAPE
MARK
1
LONG 40
LONG
SHORT 40
TAPE
MARK
LONG 20
SHORT 20
1-1. INFORMATION
BLOCK
128 bytes
1
DATA BLOCK
29
READ POINT
i
SHORT
(HIGH) 240,.S
(LOW)
278,.S
LONG
(HIGH) 470,.S
(LOW)
494,.S
READ POINT
379,.S
the signal rising edge. Data are recorded in repetition of
LONG and SHORT, and the same data are written twice.
Check
SHORT
INFORMATION
Check
SHORT
sum,
1
256
BLOCK
sum,
1
2 bytes
bytes
128 bytes
2 bytes
5 seconds
LONG
LONG
11000
Check
SHORT
DATA
Check
sum
1
256
BLOCK
sum,
1
2 bytes
bytes
2 bytes
LONG
LONG

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