Manual Number: 40110-005-2
Page 21
DRQ[7::5], DRQ[3::0] (I)
DMA Requests DRQ[7::5] and DRQ[3::0] are asynchronous channel requests used by peripheral
devices and the I/O channel microprocessors to gain DMA service (or control of the system).
They are prioritized, with DRQ0 having the highest priority and DRQ7 having the lowest. A
request is generated by bringing a DRQ line to an active level. A DRQ line must be held high
until the corresponding DMA Request Acknowledge (DAK) line goes active. DRQ[3::0] will
perform 8-bit DMA transfers; DRQ[7::5] will perform 16-bit transfers.
IO16# (I)
I/O 16-bit Chip Select (IO16#) signals the system board that the present data transfer is a 16-bit,
1 wait-state, I/O cycle. It is derived from an address decode. IO16# is active low and should be
driven with an open collector or tri-state driver capable of sinking 20 mAmps.
IOCHK# (I)
I/O Channel Check (IOCHK#) provides the system board with parity (error) information about
memory or devices on the I/O channel. When this signal is active, it indicates an uncorrectable
system error.
IORC# (I/O)
I/O Read (IORC#) 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.
IOWC# (I/O)
I/O Write (IOWC#) 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.
IRQ[15::14], IRQ[12::9], IRQ[7::3] (I)
Interrupt Requests IRQ[15::14], IRQ[12::9] and IRQ[7::3] are used to signal the microprocessor
that an I/O device needs attention. The interrupt requests are prioritized, with IRQ[15::14] and
IRQ[12::9] having the highest priority (IRQ9 is the highest) and IRQ[7::3] 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).
LA[23::17] (I/O)
These signals (unlatched) are used to address memory and I/O devices within the system. They
give the system up to 16MB of addressability. These signals are valid when BALE is high.
LA[23::17] are not latched during microprocessor cycles and therefore do not stay valid for the
whole cycle. Their purpose is to generate memory decodes for 1 wait-state memory cycles.
These decodes should be latched by I/O adapters on the falling edge of BALE. These signals
also may be driven by other microprocessors or DMA controllers that reside on the I/O channel.
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