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Revision 1.1
G
Signal Definitions
(Continued)
STOP#
M25
I/O
Target Stop.
STOP# is asserted to indicate that the cur-
rent target is requesting that the master stop the current
transaction. This signal is used with DEVSEL# to indicate
retry, disconnect, or target abort. If STOP# is sampled
active by the master, FRAME# is deasserted and the
cycle is stopped within three PCI clock cycles. As an
input, STOP# can be asserted in the following cases:
1)
If the PCI write buffers are full or if a previously buff-
ered cycle has not completed.
2)
On read cycles that cross cache line boundaries.
This is conditional based upon the programming of
GX1 module’s PCI Configuration Register, Index
41h[1].
D15
DEVSEL#
N26
I/O
Device Select.
DEVSEL# indicates that the driving
device has decoded its address as the target of the cur-
rent access. As an input, DEVSEL# indicates whether
any device on the bus has been selected. DEVSEL# is
also driven by any agent that has the ability to accept
cycles on a subtractive decode basis. As a master, if no
DEVSEL# is detected within and up to the subtractive
decode clock, a master abort cycle is initiated (except for
special cycles which do not expect a DEVSEL#
returned).
BHE#
PERR#
J24
I/O
Parity Error.
PERR# is used for reporting data parity
errors during all PCI transactions except a Special Cycle.
The PERR# line is driven two PCI clocks after the data in
which the error was detected. This is one PCI clock after
the PAR that is attached to the data. The minimum dura-
tion of PERR# is one PCI clock for each data phase in
which a data parity error is detected. PERR# must be
driven high for one PCI clock before being placed in TRI-
STATE. A target asserts PERR# on write cycles if it has
claimed the cycle with DEVSEL#. The master asserts
PERR# on read cycles.
---
SERR#
L25
I/O
System Error.
SERR# can be asserted by any agent for
reporting errors other than PCI parity, so that the PCI
central agent notifies the processor. When the Parity
Enable bit is set in the Memory Controller Configuration
register, SERR# is asserted upon detection of a parity
error in read operations from DRAM.
---
REQ3#
T24
I
Request Lines.
Indicates to the arbiter that an agent
requires the bus. Each master has its own REQ# line.
REQ# priorities are based on the specified arbitration
scheme.
---
REQ2#
AC26
---
REQ1#
AA25
---
REQ0#
AA26
---
GNT3#
AC25
O
Grant Lines.
Indicate to the requesting master that it has
been granted access to the bus. Each master has its own
GNT# line. GNT# can be retracted at any time a higher
REQ# is received or if the master does not begin a cycle
within a minimum period of time (16 PCI clocks).
---
GNT2#
U24
---
GNT1#
AD25
CLKSEL1 (Strap)
GNT0#
AB26
LPC_ROM
(Strap)
2.4.4
PCI Bus Interface Signals (Continued)
Signal Name
Ball No.
Type
Description
Mux