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the interrupt line would remain high for lack of any
strobe signal to affect it.
The input ports also have one strobe line and one inter
rupt line each.
ports also has an on-board pull-up resistor.
line is not connected or if it is driven high, the data
in the latch will follow the input lines.
can read input from the input lines.
input from the input lines and it will read the data that
is present at the instant that the input instruction is
executed.
is present on the input lines at the falling edge of the
strobe lines is latched into the input latch and remains
there as long as the strobe line is held low.
the strobe line is raised, the data in the latch will again
follow the input lines.
lines the interrupt line will change from high to low.
This can be jumpered to the IMSAI 8080 priority interrupt
lines to create an interrupt to the processor, and/or it
may be used as an indication that the processor has not
yet read the latched data.
being held low, the processor reads data from the input
port, then the interrupt line will return high at the
trailing edge of the read strobe, thus indicating to the
peripheral device that the processor has read that data and
the latch is available for latching the next data byte'
into it.
and interrupt line.
rately.
All four of the output port strobe, interrupt and data lines
appear on the 50 pin connector on the upper left edge of
the board, and all four of the input port strobe, interrupt
and data lines appear on the 50 pin connector on the upper
right hand edge of the board.
Also appearing on these connectors is ground and +5 volts.
See the schematic diagram for pin numbers.
Both the input and the output connectors are designed to
accept 3M-type flat cable board edge connectors.
flat cable may be run directly from the peripheral in
through the flat cable clamp at the top back of the IMSAI
8080 Cabinet and directly to the edge connector which slips
onto the top of the PIO 4 board.
8
20
Each of the strobe lines for the input
When the strobe line is made low the data that
Each input
and each output port has its own strobe
They may be driven together or sepa
PIO 4, Rev. 2
User Guide
The program can read
On the falling edge of the strobe
If, while the strobe line is
If the strobe
The program
As soon as
The
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