USB2513 datasheet(34/48 Pages) SMSC

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USB 2.0 High-Speed 3-Port Hub Controller

Datasheet

Revision 1.98 (11-19-07)

SMSC USB2513

DATASHEET

4.4

SMBus Slave Interface

Instead of loading User-Defined Descriptor data from an external EEPROM, the SMSC Hub can be

configured to receive a code load from an external processor via an SMBus interface. The SMBus

interface shares the same pins as the EEPROM interface; if CFG_SEL1 & CFG_SEL0 activates the

SMBus interface, external EEPROM support is no longer available (and the user-defined descriptor

data must be downloaded via the SMBus). Due to system issues, the SMSC Hub waits indefinitely for

the SMBus code load to complete and only “appears” as a newly connected device on USB after the

code load is complete.

The Hub’s SMBus implementation is a subset of the SMBus interface to the host. The device is a

slave-only SMBus device. The implementation in the device is a subset of SMBus since it only supports

two protocols.

The Write Block and Read Block protocols are the only valid SMBus protocols for the Hub. The Hub

responds to other protocols as described in Section 4.4.2, "Invalid Protocol Response Behavior," on

page 35. Reference the System Management Bus Specification, Rev 1.0.

The SMBus interface is used to read and write the registers in the device. The register set is shown

in Section 4.3.1, "Internal Register Set (Common to EEPROM and SMBus)," on page 19.

4.4.1

Bus Protocols

Typical Write Block and Read Block protocols are shown below. Register accesses are performed

using 7-bit slave addressing, an 8-bit register address field, and an 8-bit data field. The shading

indicates the Hub driving data on the SMBDATA line; otherwise, host data is on the SDA/SMBDATA

line.

The slave address is the unique SMBus Interface Address for the Hub that identifies it on SMBus. The

the data that the host is attempting to write to the register or the contents of the register that the host

is attempting to read.

Note: Data bytes are transferred MSB first (msb first).

4.4.1.1

Block Read/Write

The Block Write begins with a slave address and a write condition. After the command code, the host

issues a byte count which describes how many more bytes will follow in the message. If a slave had

20 bytes to send, the first byte would be the number 20 (14h), followed by the 20 bytes of data. The

byte count may not be 0. A Block Read or Write is allowed to transfer a maximum of 32 data bytes.

Note: For the following SMBus tables:

Figure 4.1 Block Write

Denotes Master-to-Slave

Denotes Slave-to-Master

Slave Address

171

...

Byte Count = N

Data byte 1

Data byte 2

Data byte N

Block Write

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