2-Port SS/HS USB Hub Controller

Datasheet

Revision 1.2 (05-31-13)

24

SMSC USB5532B

DATASHEET

5.2

SMBus Slave Interface

The SMBus slave interface is enabled when pull-up resistors are detected on both SM_DAT and

SM_CLK for the first millisecond after reset. For operation in SMBus Legacy Mode, an additional pull-

up resistor is required on TRST. If the SMBus interface is enabled, then the USB5532B will wait

indefinitely for the SMBus host to configure the device. Once SMBus configuration is complete, device

initialization will proceed. To disable the SMBus, a pull-down resistor of 10 K

SM_DAT. If SMBus is disabled, the device proceeds directly to device initialization using the internal

OTP ROM.

5.2.1

Pull-Up Resistor for SMBus

External pull-up resistors (10 k

Ω recommended) are required on the SM_DAT and SM_CLK pins when

implementing either SMBus mode.

Figure 5.11 SMBus Slave Connection

5.2.2

Protocol Implementation

Typical block write and block read protocols are shown in Figure 5.12 and Figure 5.13. SMBus RAM

buffer offset accesses are performed using 7-bit slave addressing, an 8- or 16-bit SMBus RAM buffer

offset field (for legacy and advanced modes, respectively), and an 8-bit data field. The shading shown

in the figures during a read or write indicates the hub is driving data on the SM_DAT line; otherwise,

host data is on the SM_DAT line.

The SMBus slave address assigned to the hub (0101100b or 0101101b) allows it to be identified on

the SMBus. The SMBus RAM buffer offset field is the internal offset in SMBus RAM to be accessed.

The data field is the data that the host is attempting to read/write from/to the SMBus RAM buffer.

Note: Data bytes are transferred MSB first.

5.2.2.1

Block Write/Read

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 zero. A block write or read allows a transfer maximum of 32 data bytes.

SMBus

Master

SM_CLK

SM_DAT

SCL

SDA

VDD

10 k

Ω

SMSC USB Hub

10 k

Ω