IBM 5150 - Page 41

clock cycles. Machine cycles (I/O or
memory) are extended
by an integral
number of clock cycles (210-ns).
-lOR
0 -I/O Read Command: This command
line instructs an
I/O device to drive its
~
data onto the data bus. It may be
driven by the microprocessor or the
DMA controller. This signal is active
low.
-lOW
0
-I/O Write Command: This command
line instructs
an I/O device to read the
data on the data bus.
It may be driven
by the microprocessor or the
DMA
controller. This signal is active low.
IRQ2-IRQ7
I Interrupt Request 2 to 7: These lines
are used to signal the microprocessor
that an
I/O device requires attention.
They are prioritized with IRQ2 as the
highest priority and IRQ7 as the
lowest.
An Interrupt Request is generated by
~
raising an IRQ line (low to high) and
holding it high until it
is acknowledged
by the microprocessor (interrupt service
routine).
-MEMR
0 -Memory Read Command: This
command line instructs the memory to
drive its data onto the data bus.
It may
be driven by the microprocessor
or the
DMA controller. This signal is active
low.
-MEMW
0
-Memory Write Command:
This
command line instructs the memory to
store the data present
on the data bus.
It may be driven by the microprocessor
r""\
or the DMA controller. This signal is
active low.
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