USB2512B-AEZG_12 Datasheet, PDF (44/63 Pages) SMSC Corporation – USB 2.0 Hi-Speed Hub Controller

USB 2.0 Hi-Speed Hub Controller
Datasheet
5.3.4
5.3.5
5.3.6
5.3.7
Stretching the SCLK Signal
The hub supports stretching of the SCLK by other devices on the SMBus. However, the hub does not
stretch the SCLK.
SMBus Timing
The SMBus slave interface complies with the SMBus Specification Revision 1.0 [3]. See Section 2.1,
AC Specifications on page 3 for more information.
Bus Reset Sequence
The SMBus slave interface resets and returns to the idle state upon a START condition followed
immediately by a STOP condition.
SMBus Alert Response Address
The SMBALERT# signal is not supported by the hub.
5.4
Default Configuration
To put the SMSC hub in the default configuration, strap CFG_SEL[1:0] to 00b. This procedure
configures the hub to the internal defaults and enables the strapping options. To place the hub in
default configuration with overrides, see Table 5.1 on page 26 for the list of the options.
The internal default values are used for the registers that are not controlled by strapping option pins.
Refer to Section 5.1 on page 27 for the internal default values that are loaded when this option is
selected. For a list of strapping option pins, see Chapter 5 on page 26, and to configure the strapping
pins, see Section 3.3.1 on page 22.
5.5
Reset
The hub experiences the following two resets:
„ Hardware reset via the RESET_N pin
„ USB bus reset
5.5.1
External Hardware RESET_N
A valid hardware reset is defined as assertion of RESET_N for a minimum of 1 μs after all power
supplies are within operating range. While reset is asserted, the hub (and its associated external
circuitry) consumes less than 500 μA of current from the upstream USB power source.
Assertion of RESET_N causes the following:
1. All downstream ports are disabled, and PRTPWR[x:1] to downstream devices is removed (unless
BC_EN[x:1] is enabled).
2. The PHYs are disabled, and the differential pairs will be in a high-impedance state.
3. All transactions immediately terminate; no states are saved.
4. All internal registers return to the default state (in most cases, 00h).
5. The external crystal oscillator is halted.
6. The PLL is halted.
The hub is operational 500 μs after RESET_N is negated. Once operational, the hub will do one of the
following, depending on configuration:
„ Read the strapping pins (default configuration with strapping options enabled)
„ Read configuration information from the external I²C EEPROM
„ Wait for configuration over SMBus.
Revision 2.2 (02-17-12)
44
DATASHEET
SMSC USB251xB/xBi