Sharp MZ-80B Owner's Manual page 121

112
lEI Interrupt Enable In (input, active high)
This signal is used to form a priority interrupt daisy chain when more than one interrupt driven device is
being used. A high level on this pin indicates that no other devices of higher priority are being serviced by a
CPU interrupt service routine.
lEO Interrupt Enable Out (output, active high)
The lEO signal is the other signal required to form a daisy chain priority scheme. It is high only ifiEI is high
and the CPU is not servicing an interrupt from this PIO. Thus this signal blocks lower priority devices from
interrupting while a higher priority device is being serviced by its CPU interrupt service routine.
INT Interrupt Request (output, open drain, active low)
When INTis active the Z-80A-PIO is requesting an interrupt from the Z-80A-CPU.
A
0 -
A
7
Port A Bus (bidirectional, tristate)
This 8 bit bus is used to transfer data and/or status or control information between Port A of the Z-80A-PIO
and a peripheral device. A
0
is the least significant bit of the Port A data bus.
A SIB Port A Strobe Pulse from Peripheral Device (input, active low)
I) Output mode: The positive edge of this strobe is issued by the peripheral to acknowledge the receipt
of data made available by the PIO.
2) Input mode: The strobe is issued by the peripheral to load data from the peripheral into the Port A
input register. Data is loaded into the PIO when this signal is active.
3) Bidirectional mode: When this signal is active, data from the Port A output register is gated onto Port
A bidirectional data bus. The positive edge of the strobe acknowledges the receipt of the data.
4) Control mode: The strobe is inhibited internally.
A RDY Register A Ready (output, active high)
The meaning of this signal depends on the mode of operation selected for Port A as follows:
I) Output mode: This signal goes active to indicate that the Port A output register has been loaded and
the peripheral data bus is stable and ready for transfer to the peripheral device.
2) Input mode: This signal is active when the Port A input register is empty and is ready to accept data
from the peripheral device.
3) Bidirectional mode: This signal is active when data is available in the Port A output register for trans-
fer to the peripheral device. In this mode data is not placed on the Port A data bus unless A SIB
is active.
4) Control mode: This signal is disabled and forced to a low state.
B
0 -
B
7
Port B Bus (bidirectional, tristate)
This 8 bit bus is used to transfer data and/or status or control information between Port B of the PIO and a
peripheral device. The Port B data bus is capable of supplying I .Sma@ I.SV to drive Darlington transistors.
B
0
is the least significant bit of the bus.
B SIB Port B Strobe Pulse from Peripheral Device (input, active low)
The meaning of this signal is similar to that of A SIB with the following exception:
In the Port A bidirectional mode this signal strobes data from the peripheral device into the Port A
input register.
B RDY Register B Ready (output, active high)
The meaning of this signal is similar to that of A Ready with the following exception:
In the Port A bidirectional mode this signal is high when the Port A input register is empty and ready
to accept data from the peripheral device.