Functional Description
222 Datasheet
5.20.7 SMBus Slave Interface
The PCH SMBus Slave interface is accessed using the SMBus. The SMBus slave logic will
not generate or handle receiving the PEC byte and will only act as a Legacy Alerting
Protocol device. The slave interface allows the PCH to decode cycles, and allows an
external microcontroller to perform specific actions. Key features and capabilities
include:
• Supports decode of three types of messages: Byte Write, Byte Read, and Host
Notify.
• Receive Slave Address register: This is the address that the PCH 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 PCH.
• Status bits to indicate that the SMBus slave logic caused an interrupt or SMI# due
to the reception of a message that matched the slave address.
— Bit 0 of the Slave Status Register for the Host Notify command
— Bit 16 of the SMI Status Register (Section 13.8.3.8) for all others
Note: The external microcontroller should not attempt to access the PCH SMBus slave logic
until either:
— 800 milliseconds after both: RTCRST# is high and RSMRST# is high, OR
— The PLTRST# deasserts
If a master leaves the clock and data bits of the SMBus interface at 1 for 50 µs or more
in the middle of a cycle, the PCH slave logic's behavior is undefined. This is interpreted
as an unexpected idle and should be avoided when performing management activities
to the slave logic.
Note: When an external microcontroller accesses the SMBus Slave Interface over the SMBus
a translation in the address is needed to accommodate the least significant bit used for
read/write control. For example, if the PCH slave address (RCV_SLVA) is left at 44h
(default), the external micro controller would use an address of 88h/89h (write/read).
5.20.7.1 Format of Slave Write Cycle
The external master performs Byte Write commands to the PCH 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.
Table 5-48 has the values associated with the registers.
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