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886LCD/ATX(GV) -/ATXU(GV)

KTD-00647-C

Public User Manual

Date: 2007-02-08 Page

43 of 71

ARBITRATION PINS (BUS MASTERS ONLY)

REQ#

Request indicates to the arbiter that this agent desires use of the bus. This is a point to point signal.
Every master has its own REQ# which must be tri-stated while RST# is asserted.

GNT#

Grant indicates to the agent that access to the bus has been granted. This is a point to point signal.
Every master has its own GNT# which must be ignored while RST# is asserted.

While RST# is asserted, the arbiter must ignore all REQ# lines since they are tri-stated and do not
contain a valid request. The arbiter can only perform arbitration after RST# is deasserted. A master
must ignore its GNT# while RST# is asserted. REQ# and GNT# are tri-state signals due to power
sequencing requirements when 3.3V or 5.0V only add-in boards are used with add-in boards that use
a universal I/O buffer.

ERROR REPORTING PINS.

The error reporting pins are required by all devices and maybe asserted when enabled
PERR#

Parity Error is only for the reporting of data parity errors during all PCI transactions except a Special
Cycle. The PERR# pin is sustained tri-state and must be driven active by the agent receiving data two
clocks following the data when a data parity error is detected. The minimum duration of PERR# is one
clock for each data phase that a data parity error is detected. (If sequential data phases each have a
data parity error, the PERR# signal will be asserted for more than a single clock.) PERR# must be
driven high for one clock before being tri-stated as with all sustained tri-state signals. There are no
special conditions when a data parity error may be lost or when reporting of an error may be delayed.
An agent cannot report a PERR# until it has claimed the access by asserting DEVSEL# (for a target)
and completed a data phase or is the master of the current transaction.

SERR#

System Error is for reporting address parity errors, data parity errors on the Special Cycle command,
or any other system error where the result will be catastrophic. If an agent does not want a non-
maskable interrupt (NMI) to be generated, a different reporting mechanism is required. SERR# is pure
open drain and is actively driven for a single PCI clock by the agent reporting the error. The assertion
of SERR# is synchronous to the clock and meets the setup and hold times of all bused signals.
However, the restoring of SERR# to the deasserted state is accomplished by a weak pullup (same
value as used for s/t/s) which is provided by the system designer and not by the signaling agent or
central resource. This pull-up may take two to three clock periods to fully restore SERR#. The agent
that reports SERR#s to the operating system does so anytime SERR# is sampled asserted.

INTERRUPT PINS (OPTIONAL).

Interrupts on PCI are optional and defined as “level sensitive,” asserted low (negative true), using open drain output
drivers. The assertion and deassertion of INTx# is asynchronous to CLK. A device asserts its INTx# line when
requesting attention from its device driver. Once the INTx# signal is asserted, it remains asserted until the device
driver clears the pending request. When the request is cleared, the device deasserts its INTx# signal. PCI defines one
interrupt line for a single function device and up to four interrupt lines for a multi-function device or connector. For a
single function device, only INTA# may be used while the other three interrupt lines have no meaning.
INTA#

Interrupt A is used to request an interrupt.

INTB#

Interrupt B is used to request an interrupt and only has meaning on a multi-function device.

INTC#

Interrupt C is used to request an interrupt and only has meaning on a multi-function device.

INTD#

Interrupt D is used to request an interrupt and only has meaning on a multi-function device.

4.23.3 886LCD/ATX(GV) and 886LCD/ATXU(GV) PCI IRQ & INT routing

Board type

Slot

IDSEL

INTA INTB INTC INTD