GX1 Datasheet, PDF (35/247 Pages) National Semiconductor (TI) – Processor Series Low Power Integrated x86 Solution

Signal Definitions (Continued)
2.2.2 PCI Interface Signals (Continued)
Signal Name
BGA SPGA
Pin No. Pin No
Type
LOCK#
B11
B16
s/t/s
(PU)
(PU)
DEVSEL#
A9
E15
s/t/s
(PU)
(PU)
PERR#
A11
D16
s/t/s
(PU)
(PU)
SERR#
C12
A17
OD
(PU)
(PU)
REQ[2:0]#
D3,
E3,
I
H3,
K2,
E3
E1
(PU)
(PU)
Description
Lock Operation
LOCK# indicates an atomic operation that may require multiple
transactions to complete. When LOCK# is asserted, nonexclusive
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 its 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 deas-
serted.
This pin is internally connected to a weak (>20-kohm) pull-up
resistor.
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 except for special
cycles which do not expect a DEVSEL# returned.
This pin is internally connected to a weak (>20-kohm) pull-up
resistor.
Parity Error
PERR# is used for the 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,
which is one SYSCLK after the PAR that was 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 going to TRI-STATE. A tar-
get 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 weak (>20-kohm) pull-up
resistor.
System Error
SERR# 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.
Request Lines
REQ# 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.
This pin is internally connected to a weak (>20-kohm) pull-up
resistor.
Revision 1.0
35
www.national.com