Functional Description
5-128
Intel
82801BA ICH2 Datasheet
5.17.4
SMBALERT#
SMBALERT# is multiplexed with GPIO[11]. When enabled and the signal is asserted, the ICH2
can generate an interrupt, an SMI#, or a wake event from S1-S4. To resume using SMBALERT#,
the SMB_SMI_EN bit must be enabled to generate an SMI (see
Section 12.1.12, “HOSTC—Host
Configuration Register (SMBUS—D31:F3)” on page 12-4
).
5.17.5
SMBus Slave Interface
The ICH2’s SMBus Slave interface is accessed via the SMLINK[1:0] signals. The slave interface
allows the ICH2 to decode cycles and allows an external microcontroller to perform specific
actions. Key features and capabilities include:
Supports decode of two messages type: Write and Read
Receive Slave Address register: This is the address that the ICH2 decodes. A default value is
provided so that the slave interface can be used without the processor having to program this
register.
Receive Slave Data register in the SMBus I/O space that includes the data written by the
external microcontroller
Registers that the external microcontroller can read to get the state of the ICH2. See
Table 5-88
Status bit to indicate that the SMBus logic caused an SMI# due to the reception of a message
that matched the slave address. See
Section 9.8.3.12
.
Format of Slave Write Cycle
The external master performs Byte Write commands to the ICH2 SMBus Slave I/F. The
“Command” field (bits 11-18) indicate which register is being accessed. The Data field (bits 20-27)
indicate the value that should be written to that register.
The Write Cycle format is shown in
Table 5-84
.
Table 5-85
lists the values associated with the
registers.
Table 5-84. Slave Write Cycle Format
Bits
Description
Driven by
Comment
1
Start Condition
External Microcontroller
2:8
Slave Address - 7 bits
External Microcontroller
Must match value in Receive Slave Address
register
9
Write
External Microcontroller
Always 0
10
ACK
ICH2
11:18
Command
External Microcontroller
This field indicates which register will be
accessed.
See
Table 5-85
below for the register
definitions
19
ACK
ICH2
20:27
Register Data
External Microcontroller
See
Table 5-85
below for the register
definitions
28
ACK
ICH2
29
Stop
External Microcontroller
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