Datasheet

USB 2.0 Hi-Speed Hub Controller
Datasheet
Revision 2.2 (02-17-12) 42 SMSC USB251xB/xBi
DATASHEET
5.2.3 Pull-Up Resistor
The circuit board designer is required to place external pull-up resistors (10 kΩ recommended) on the
SDA/SMBDATA and SCL/SMBCLK/CFG_SEL[0] lines (per
SMBus 1.0 Specification [3], and EEPROM
manufacturer guidelines) to VDD33 in order to assure proper operation.
5.2.4 In-Circuit EEPROM Programming
The EEPROM can be programmed via automatic test equipment (ATE) by pulling RESET_N low (which
tri-states the hub’s EEPROM interface and allows an external source to program the EEPROM).
5.3 SMBus
The SMSC hub can be configured by an external processor via an SMBus interface (see Ta bl e 5.1 for
details on enabling the SMBus interface). The SMBus interface shares the same pins as the EEPROM
interface, and therefore the hub no longer supports the I
2
C EEPROM interface when the SMBus
interface has been enabled. 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 acts as a slave-only SMBus device. The implementation only supports block write
(Section 5.3.2.1) and block read (Section 5.3.2.2) protocols, where the available registers are outlined
in Section 5.1 on page 27. Reference the
System Management Bus Specification [3] for additional
information.
5.3.1 SMBus Slave Address
The 7-bit slave address is 0101100b. The hub will not respond to the general call address of 0000000b.
5.3.2 Protocol Implementation
Typical block write and block read protocols are shown in figures 5.1 and 5.2. Register accesses are
performed using 7-bit slave addressing, an 8-bit register address field, 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 SMBDATA
line; otherwise, host data is on the SDA/SMBDATA line.
The SMBus slave address assigned to the hub (0101100b) allows it to be identified on the SMBus.
The register address field is the internal address of the register to be accessed. The register data field
is 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.