GXM datasheet(28/244 Pages) NSC

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Signal Definitions (Continued)

LOCK#

B11

(PU)

B16

(PU)

s/t/s

Lock Operation

LOCK# indicates an atomic operation that may require multiple

transactions to complete. When LOCK# is asserted, nonexclu-

sive transactions may proceed to an address that is not currently

locked (at least 16 bytes must be locked). A grant to start a trans-

action on PCI does not guarantee control of LOCK#. Control of

LOCK# is obtained under it own protocol in conjunction with

GNT#. It is possible for different agents to use PCI while a single

master retains ownership of LOCK#. The arbiter can implement

a complete system lock. In this mode, if LOCK# is active, no

other master can gain access to the system until the LOCK# is

deasserted.

This pin is internally connected to a 20-kohm pull-up resistor.

DEVSEL#

(PU)

E15

(PU)

s/t/s

Device Select

DEVSEL# indicates that the driving device has decoded its

address as the target of the current access. As an input,

DEVSEL# indicates whether any device on the bus has been

selected. DEVSEL# will also be driven by any agent that has the

ability to accept cycles on a subtractive decode basis. As a mas-

ter, if no DEVSEL# is detected within and up to the subtractive

decode clock, a master abort cycle will result expect for special

cycles which do not expect a DEVSEL# returned.

This pin is internally connected to a 20-kohm pull-up resistor.

PERR#

A11

(PU)

D16

(PU)

s/t/s

Parity Error

PERR# is used for reporting of data parity errors during all PCI

transactions except a Special Cycle. The PERR# line is driven

two SYSCLKs after the data in which the error was detected.

This is one SYSCLK after the PAR that is attached to the data.

The minimum duration of PERR# is one SYSCLK for each data

phase in which a data parity error is detected. PERR# must be

driven high for one SYSCLK before being in TRI-STATE mode. A

target asserts PERR# on write cycles if it has claimed the cycle

with DEVSEL#. The master asserts PERR# on read cycles.

This pin is internally connected to a 20-kohm pull-up resistor.

SERR#

C12

(PU)

A17

(PU)

System Error

System Error may be asserted by any agent for reporting errors

other than PCI parity. The intent is to have the PCI central agent

assert NMI to the processor. When the Parity Enable bit is set in

the Memory Controller Configuration register, SERR# will be

asserted upon detecting a parity error on read operations from

DRAM.

REQ[2:0]#

D3,

H3,

(PU)

E3,

K2,

(PU)

Request Lines

Request indicates to the arbiter that an agent desires use of the

bus. Each master has its own REQ# line. REQ# priorities are

based on the arbitration scheme chosen.

Each of these pins are internally connected to a 20-kohm pull-up

resistor.

2.2.2

PCI Interface Signals (Continued)

Signal Name

BGA

Pin No.

SPGA

Pin No

Type

Description

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