55
•
For
key interruption
As
stated above, in the MZ-80B, key interruptions can be received by PIO control. Illustrated
below are exampl
es
of
simple key interrupt and response settings.
Try to program the machine
so
that interrupt routine $5080
is
called the
moment
the [
BRE
AK
I
key
is
pressed . In this example the address table
of
th
e interrupt routine
is
set to $3370 and the
vector interrupt
of
interrupt mode 2
is
used. Also, the PIO
is
set in mode 3 and no handshake bus
is
used.
As
shown in Table 4.5,
the
[ B
RE
AK I key is indicated during keyscan
by
strobe signal 3H and
bit
data
7 (7FH). Therefore,
the
strobe signal must be set
to
3H and
the
interru
pt
mask must be set
to
7FH.
It
is
also necessary
to
set 70H in the 8-bit
interrupt
vector (LSB being
'0')
.
The setting codes used
so
far are as follows:
LD A, 33H
LD I, A
IM
2
LD
HL,
5080H
LD
(3370H), HL
LD A,
70H
OUT
(EBH), A
LD
A, CFH
OUT
(EBH), A
LD A,
FFH
OUT
(EBH), A
LD A, 97H
OUT
(EBH), A
LD A, 7FH
OUT
(EBH), A
IN
A, (E8H)
AND
FOH
OR 13H
OUT
(E8H), A
) Setting
of
vector register
)
setting
of
interrupt mode 2
} Setting the address
of
the
interrupt
routine in
the
interrupt address
}
setting
the
interrupt
vector (8-bits)
} Setting
port
B in mode 3
} Setting all
port
B terminals in the
input
mode
}
setting
of
int
errupt
control words,
or
enabli
ng
interruptions
}
Setting
of
mask words;
bit
data 7
(MSB
being 'L')
is
masked by writing
7FH
)
Setting
of
the
key strobe delivered
to
port
A
to
3H. The strobe gate is
opened with A4 set
to
'H'
After setting modes
as
described above,
the
address table at $3370 is referenced
by
the vector
interrupt
when the [ B
REAK
I key
is
pushed at any point, and
interrupt
routine $5080 is called.
After
the
interrupt
routine
is completed, the instruction used
to
return control
to
the
main pro-
gramisRETI.
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