Functional Description
216 Datasheet
The PCH supports the System Management Bus (SMBus) Specification, Version 2.0.
Slave functionality, including the Host Notify protocol, is available on the SMBus pins.
The SMLink and SMBus signals can be tied together externally depending on TCO mode
used. Refer to Section 5.14.2 for more details.
Using the SMB host controller to send commands to the PCH SMB slave port is not
supported.
5.20.1.1 Command Protocols
In all of the following commands, the Host Status Register (offset 00h) is used to
determine the progress of the command. While the command is in operation, the
HOST_BUSY bit is set. If the command completes successfully, the INTR bit will be set
in the Host Status Register. If the device does not respond with an acknowledge, and
the transaction times out, the DEV_ERR bit is set. If software sets the KILL bit in the
Host Control Register while the command is running, the transaction will stop and the
FAILED bit will be set.
Quick Command
When programmed for a Quick Command, the Transmit Slave Address Register is sent.
The PEC byte is never appended to the Quick Protocol. Software should force the
PEC_EN bit to 0 when performing the Quick Command. Software must force the
I2C_EN bit to 0 when running this command. See section 5.5.1 of the System
Management Bus (SMBus) Specification, Version 2.0 for the format of the protocol.
Send Byte / Receive Byte
For the Send Byte command, the Transmit Slave Address and Device Command
Registers are sent. For the Receive Byte command, the Transmit Slave Address Register
is sent. The data received is stored in the DATA0 register. Software must force the
I2C_EN bit to 0 when running this command.
The Receive Byte is similar to a Send Byte, the only difference is the direction of data
transfer. See sections 5.5.2 and 5.5.3 of the System Management Bus (SMBus)
Specification, Version 2.0 for the format of the protocol.
Write Byte/Word
The first byte of a Write Byte/Word access is the command code. The next 1 or 2 bytes
are the data to be written. When programmed for a Write Byte/Word command, the
Transmit Slave Address, Device Command, and Data0 Registers are sent. In addition,
the Data1 Register is sent on a Write Word command. Software must force the I2C_EN
bit to 0 when running this command. See section 5.5.4 of the System Management Bus
(SMBus) Specification, Version 2.0 for the format of the protocol.
Read Byte/Word
Reading data is slightly more complicated than writing data. First the PCH must write a
command to the slave device. Then it must follow that command with a repeated start
condition to denote a read from that device's address. The slave then returns 1 or 2
bytes of data. Software must force the I2C_EN bit to 0 when running this command.
When programmed for the read byte/word command, the Transmit Slave Address and
Device Command Registers are sent. Data is received into the DATA0 on the read byte,
and the DAT0 and DATA1 registers on the read word. See section 5.5.5 of the System
Management Bus (SMBus) Specification, Version 2.0 for the format of the protocol.
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