![](http://datasheet.mmic.net.cn/330000/INTEL82801_datasheet_16416407/INTEL82801_30.png)
Signal Description
2-2
82801AA and 82801AB Datasheet
2.3
PCI Interface
Table 2-3. PCI Interface Signals (Sheet 1 of 3)
Name
Type
Description
AD[31:0]
I/O
PCI Address/Data:
AD[31:0] is a multiplexed address and data bus. During the first
clock of a transaction, AD[31:0] contain a physical address (32 bits). During
subsequent clocks, AD[31:0] contain data. The ICH drives all 0’s on AD[31:0] during the
address phase of PCI Interrupt Acknowledge cycles.
C/BE[3:0]#
I/O
Bus Command and Byte Enables:
The command and byte enable signals are
multiplexed on the same PCI pins. During the address phase of a transaction,
C/BE[3:0]# define the bus command. During the data phase, C/BE[3:0]# define the
Byte Enables.
C/BE[3:0]#
Command Type
0 0 0 0
Interrupt Acknowledge
0 0 0 1
Special Cycle
0 0 1 0
I/O Read
0 0 1 1
I/O Write
0 1 1 0
Memory Read
0 1 1 1
Memory Write
1 0 1 0
Configuration Read
1 0 1 1
Configuration Write
1 1 0 0
Memory Read Multiple
1 1 1 0
Memory Read Line
1 1 1 1
Memory Write and Invalidate
NOTE:
All command encodings not shown are reserved. The ICH does not decode
reserved values, and, therefore, does not respond if a PCI master generates a
cycle using one of the reserved values.
DEVSEL#
I/O
Device Select:
The ICH asserts DEVSEL# to claim a PCI transaction. As an output,
the ICH asserts DEVSEL# when a PCI master peripheral attempts an access to an
internal ICH register or man memory. As an input, DEVSEL# indicates the response to
an ICH-initiated transaction on the PCI bus. DEVSEL# is tri-stated from the leading
edge of PCIRST#. DEVSEL# remains tri-stated by the ICH until driven by a Target
device.
FRAME#
I/O
Cycle Frame:
The current Initiator drives FRAME# to indicate the beginning and
duration of a PCI transaction. While the initiator asserts FRAME#, data transfers
continue. When the initiator negates FRAME#, the transaction is in the final data
phase. FRAME# is an input to the ICH when the ICH is the target, and FRAME# is an
output from the ICH when the ICH is the Initiator. FRAME# remains tri-stated by the
ICH until driven by an Initiator.
IRDY#
I/O
Initiator Ready:
IRDY# indicates the ICH's ability, as an Initiator, to complete the
current data phase of the transaction. It is used in conjunction with TRDY#. A data
phase is completed on any clock both IRDY# and TRDY# are sampled asserted.
During a write, IRDY# indicates the ICH has valid data present on AD[31:0]. During a
read, it indicates the ICH is prepared to latch data. IRDY# is an input to the ICH when
the ICH is the Target and an output from the ICH when the ICH is an Initiator. IRDY#
remains tri-stated by the ICH until driven by an Initiator.
TRDY#
I/O
Target Ready:
TRDY# indicates the ICH's ability as a Target to complete the current
data phase of the transaction. TRDY# is used in conjunction with IRDY#. A data phase
is completed when both TRDY# and IRDY# are sampled asserted. During a read,
TRDY# indicates that the ICH, as a Target, has placed valid data on AD[31:0]. During a
write, TRDY# indicates the ICH, as a Target is prepared to latch data. TRDY# is an
input to the ICH when the ICH is the Initiator and an output from the ICH when the ICH
is a Target. TRDY# is tri-stated from the leading edge of PCIRST#. TRDY# remains tri-
stated by the ICH until driven by a target.