Advertisement
USER GUIDE
The PIO 4 Board has four input ports and four output ports.
Each port has an eight bit latch associated with it.
ports may be addressed in one of two different ways: First,
addressed as an input/output port with input or output in
structions; second, they may be addressed with memory refer
ence instructions.
jumpers and the board cannot have both types of addressing
at the same time.
addresses that are four sequential addresses and the four
output ports form a block of four sequential addresses which
are the same four addresses as the input port.
w o r d s , the same address used with an input instruction to
input on port number
port number
.
0
When the board is being used with memory-mapped I/O, arty 8080
instruction which either reads or writes a byte from memory
can be used to either read or write respectively
an input or output port on the I/O board.
accumulator, from the address that this board is jumper-
selected to respond to, will load the accumulator with the
data from the input port addressed.
and each of the four output latches are equipped with data
strobe lines.
Each port has both an interrupt line and a
strobe line which can be used as hand-shake signals for
conventional parallel data transfers.
output ports, a low pulse on the strobe line will set the
interrupt line low.
falling edge of the strobe line and the strobe line would
normally be kept high.
The interrupt line is made high again upon the trailing
edge of the WRITE strobe of the processor which is writing
a new eight bits of data into the output port.
strobe line would be the input hand-shaking line and the
interrupt line would be the output hand-shaking line.
interrupt line may also be jumpered to one of the IMSAI
8080 priority interrupt lines on the back plane to effect
an interrupt to the processor when it goes low, that is,
when the strobe line has been pulsed low to indicate it has
been taken' by the peripheral device.
If it is not desired to use hand-shaking lines, it is not
necessary to jumper them or take any other action. Success
ive bits may be put out to the output ports with no further
action by any other device.
would remain high from, the on-board.pull-up resistor and
The type of addressing is selectable by
The four input ports form a block of
is the same address used to output on
0
The interrupt line changes on the
In this case, the strobe line
PIO 4, Rev. 2
User Guide
In other
a
byte from
That is, a load
Each of the four input
In the case of the
Thus, the
These
The
8 - 1 9
Advertisement
