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2-Port USB 2.0 Hub Controller
Datasheet
SMSC USB2502 25 Revision 2.3 (08-27-07)
DATASHEET
5.3.1.1 Byte Protocols
When using the Hub SMBus Interface for byte transfers, a write will always consist of the SMBus
Interface Slave Address byte, followed by the Internal Address Register byte, then the data byte.
The normal read protocol consists of a write to the HUB with the SMBus Interface Address byte,
followed by the Internal Address Register byte. Then restart the Serial Communication with a Read
consisting of the SMBus Interface Address byte, followed by the data byte read from the Hub. This
can be accomplished by using the Read Byte protocol.
Note: For the following SMBus tables:
Write Byte
The Write Byte protocol is used to write data to the registers. The data will only be written if the protocol
shown in Table 5.2 is performed correctly. Only one byte is transferred at a time for a Write Byte
protocol.
Read Byte
The Read Byte protocol is used to read data from the registers. The data will only be read if the
protocol shown in Table 5.3 is performed correctly. Only one byte is transferred at a time for a Read
Byte protocol.
5.3.2 Invalid Protocol Response Behavior
Registers that are accessed with an invalid protocol are not updated. A register is only updated
following a valid protocol. The only valid protocols are Write Byte and Read Byte, which are described
above.
The Hub only responds to the hardware selected Slave Address.
Attempting to communicate with the Hub over SMBus with an invalid slave address or invalid protocol
results in no response, and the SMBus Slave Interface returns to the idle state.
The only valid registers that are accessible by the SMBus slave address are the registers defined in
the Registers Section. See Section 5.3.3 for the response to undefined registers.
5.3.3 General Call Address Response
The Hub does not respond to a general call address of 0000_000b.
Table 5.2 SMBus Write Byte Protocol
Field: Start Slave Addr Wr Ack Reg. Addr Ack Reg. Data Ack Stop
Bits:1 71181811
Table 5.3 SMBus Read Byte Protocol
Field: Start Slave
Addr
Wr Ack Reg.
Addr
Ack Start Slave
Addr
Rd Ack Reg.
Data
Nack Stop
Bits: 1 7 1 1 8 1 1 7 1 1 8 1 1
Denotes Master-to-Slave Denotes Slave-to-Master