IBM 5170 Technical Reference page 42

I/O eH RDY
(I)
'I/O channel ready' is pulled low (not ready) by a memory or
I/O device to lengthen I/O or memory cycles. Any slow device
using this line should drive it low immediately upon detecting its
valid address and a Read or Write command. Machine cycles are
extended by an integral number of clock cycles (167
nanoseconds). This signal should be held low for no more than
2.5 microseconds.
IRQ3-IRQ7, IRQ9-IRQI2 and IRQ 14 through 15
(I)
Interrupt Requests 3 through 7, 9 through 12, and 14 through 15
are used to signal the microprocessor that an I/O device needs
attention. The interrupt requests are prioritized, with IRQ9
through IRQ12 and IRQ14 through IRQ15 having the highest
priority (IRQ9 is the highest) and IRQ3 through IRQ7 having the
lowest priority (IRQ7 is the lowest). An interrupt request is
generated when an IRQ line is raised from low to high. The line
must be held high until the microprocessor acknowledges the
interrupt request (Interrupt Service routine). Interrupt 13 is used
on the system board and is not available on the I/O channel.
~
Interrupt 8 is used for the real-time clock.
-lOR (I/O)
'-I/O Read' instructs an I/O device to drive its data onto the
data bus.
It
may be driven by the system microprocessor or DMA
controller, or by a microprocessor or DMA controller resident on
the I/O channel. This signal is active low.
-lOW (I/O)
'-I/O Write' instructs an I/O device to read the data on the
data bus. It may be driven by any microprocessor or DMA
controller in the system. This signal is active low.
1-24 System Board