Sharp MZ-800 Service Manual page 34

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
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Bo-B, 27-34
1/0 Port B Bus
BSiB
17
I Port B Strobe
f----
BRDY 21
0 Register B Ready
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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.
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Data transfer is carried out with the PlO and peripheral
device via this bus. AD is the least significant digit.
I Port A strobe.
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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.
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2) Byte input mode
: Peripheral device loads data in the
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PlO port A input data register at a
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rising edge of this strobe.
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3) Bidirectional mode : The contents of the port A output
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data register are outputted on
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AO-A7 when the strobe is in low
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state.
~tmode
: Not used .
..
~~----------~
..
-~
- ._._-------
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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