Datasheet

USB 2.0 Hi-Speed Hub Controller
Datasheet
SMSC USB251xB/xBi 41 Revision 2.2 (02-17-12)
DATASHEET
5.1.32 Register FFh: Status/Command
5.2 I
2
C EEPROM
The SMSC hub can be configured via a 2-wire (I
2
C) EEPROM (256x8). See Tab le 5. 1 for details on
enabling the I
2
C EEPROM interface. The I
2
C EEPROM interface implements a subset of the I
2
C
Master Specification
(refer to the Philips Semiconductor Standard I
2
C-Bus Specification I
2
C protocol
for details). The hub’s interface is designed to attach to a single dedicated I
2
C EEPROM which
conforms to the Standard-mode I
2
C specification (100 kbit/s transfer rate and 7-bit addressing) for
protocol and electrical compatibility. The I
2
C EEPROM shares the same pins as the SMBus interface,
therefore the SMBus interface is not available when the I
2
C EEPROM interface has been enabled (and
vice versa).
The hub acts as the master and generates the serial clock SCL, controls the bus access (determines
which device acts as the transmitter and which device acts as the receiver), and generates the START
and STOP conditions. The hub will read the external EEPROM for configuration data and then attach
to the upstream USB host.
Note: If no external EEPROM is present, the hub will write 0 to all configuration registers.
The hub does not have the capacity to write to the external EEPROM. The hub only has the capability
to read from an external EEPROM. The external EEPROM will be read (even if it is blank), and the
hub will be configured with the values that are read. Any values read for unsupported registers will not
be retained (i.e., they will remain as the default values). Reserved registers should be set to
0 unless
otherwise specified. EEPROM reset values are 0x00. Contents read from unavailable registers should
be ignored.
Note: Go to www.smsc.com, search for USB251xB and select e2prommap.msi from the documents
section to download the EEPROM data configuration utility tool.
5.2.1 I
2
C Slave Address
The 7-bit slave address is 0101100b.
Note: 10-bit addressing is not supported.
5.2.2 Protocol Implementation
The hub will only access an EEPROM using the sequential read protocol as outlined in Chapter 8 of
MicroChip 24AA02/24LC02B [4].
BIT
NUMBER BIT NAME DESCRIPTION
7:3 rsvd
2 INTF_PW_DN SMBus Interface Power Down:
0 : interface is active
1 : interface power down after ACK has completed
1 RESET Reset the SMBus interface and internal memory back to RESET_N assertion
default settings.
0 : normal run/idle state
1 : force a reset of registers to their default state
0 USB_ATTACH USB Attach (and write protect)
0 : SMBus slave interface is active
1 : the hub will signal a USB attach event to an upstream device, and the
internal memory (address range 0x00-0xFE) is write-protected to prevent
unintentional data corruption.