Datasheet

USB 2.0 Hi-Speed Hub Controller
Datasheet
Revision 2.2 (02-17-12) 26 SMSC USB251xB/xBi
DATASHEET
Chapter 5 Initial Interface/Configuration Options
The hub must be configured in order to correctly function when attached to a USB host controller. The
hub can be configured either internally or externally by setting the CFG_SEL[1:0] pins (immediately
after RESET_N negation) as outlined in the table below.
Note: See Chapter 11 (Hub Specification) of the USB specification for general details regarding hub
operation and functionality.
To configure the hub externally, there are two principal ways to interface to the hub: over SMBus or
I
2
C EEPROM. The hub can be configured internally, where several default configurations are available
as described in the table below. When configured internally, additional configuration is available using
the strap options (listed in Section 3.3.1 on page 22).
Note: Strap options are not available when configuring the hub over I
2
C or SMBus.
Table 5.1 Initial Interface/Configuration Options
CFG_SEL[1] CFG_SEL[0] DESCRIPTION
0 0 Default configuration:
 Strap options enabled
 Self-powered operation enabled
 Individual power switching
 Individual over-current sensing
0 1 The hub is configured externally over SMBus (as an SMBus slave
device):
 Strap options disabled
 All registers configured over SMBus
1 0 Default configuration with the following overrides:
 Bus-powered operation
1 1 The hub is configured over 2-wire I
2
C EEPROM:
 Strap options disabled
 All registers configured by I
2
C EEPROM