Service manual
MZ-800
Pin name Pin No.
1/0
Signal
name
TNT
23 0
Interrupt
Request
Ao-A,
15-12
1/0
Port A Bus
10-
7
ASTB
16
I Port A
Strobe
ARDY
18
0
Register A Ready
I
Bo-B,
27-34
1/0
Port B Bus
BSiB
17
I Port B
Strobe
f----
BRDY
21
0
Register B Ready
I
I
For the MZ-800 the PlO located on the
1/0
space, and
address
of
ports
performs
the
following:
$FC
Port A control
Description
Connection
with
CPU INT signal.
A
low
on
this
line causes
the
PlO
to
place an
interrupt
request
to
the
CPU. Because
it
is
of
an open drain type,
it
is
possible
to
make INT
of
several peripheral
LSI
wired
OR
using
the
pullup
resistance.
--
Port A data bus.
I
Data
transfer
is carried
out
with
the
PlO and peripheral
device via
this
bus.
AD
is
the
least
significant
digit.
I
Port A strobe.
I
Significance
of
this
signal depends on
the
Port A operation-
al
mode.
•
1)
Byte
output
mode
:
It
indicates
that
the
peripheral de-
vice has received data
from
the
PlO
at
a
riding
edge
of
this
strobe.
I
2)
Byte
input
mode
: Peripheral device loads data in the
I
PlO
port
A
input
data register
at
a
!
I
rising edge
of
this
strobe.
I
3) Bidirectional
mode
:
The
contents
of
the
port
A
output
I
I
data register are
outputted
on
I
AO-A7
when
the
strobe
is in
low
I
state.
~tmode
:
Not
used .
..
~~----------~
..
-~
-
._._-------
I
I
I
I
I
I
I
I
I
33
Register A ready.
Significance
of
this
signal depends ot!
the
state
of
the
port
A
operational
mode.
1) Byte
output
mode
: Data are loaded in
the
port
A data
output
register
when
this
signal
goes
high,
makes
AO-A7
stable,
and
it
indicates
that
data can be
transferred
to
a peripheral device.
2) Byte
input
mode
: A
high
on
this
line indicates
that
the
port
A data
input
register is
not
occupied
so as
to
be ready
for
receiving
of
a
next
data
into
the
data register.
3)
Bidirectional
mode
:
This
signal is used
to
indicate
that
data has been ready in the
port
A
output
data register. Data
will
not
be issued
on
AO-A7
in
this
mode,
unless
ASTB
turns
low.
4)
Bit
mode
:
Not
used.
Port B data bus.
Function
of
this
bus is identical
to
AO-A7.
But,
it
permits
to
drive
a
Darlington
transistor
as
the
bus
can
supply
1.5
V,
1.5
mA.
BD
is
the
least
significant
digit.
Port B strobe.
Function
of
this
signal is identical
to
ASTB, except
for
the
following:
This
signal is used
to
load
data
from
a peripheral device
into
the
port
A
input
data register,
when
the
port
A is in
the
bidirectional
mode.
Register B ready.
Function
of
this
signal is identical
to
ARDY, except
for
the
following:
This
signal indicates
that
the
port
A
input
data register is
unoccupied
and is ready
for
receiving
of
a
next
data,
when
the
port
A is in
the
bidirectional
mode.
$FD
$FE
$FF
Port B
control
Port A data
Port B data