SMSC USB2514 - Manual (Page 38)

USB 2.0 High-Speed 4-Port Hub Controller
Datasheet
Revision 1.98 (11-19-07) 38 SMSC USB2514
DATASHEET
Figure 4.3 LED Strapping Option
4.7 Reset
There are two different resets that the Hub experiences. One is a hardware reset (either from the
internal POR reset circuit or via the RESET_N pin) and the second is a USB Bus Reset.
4.7.1 Internal POR Hardware Reset
All reset timing parameters are guaranteed by design.
4.7.2 External Hardware RESET_N
A valid hardware reset is defined as assertion of RESET_N for a minimum of 1us 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 (external pin) causes the following:
1. All downstream ports are disabled, and PRTPWR power to downstream devices is removed.
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, 00(h)).
5. The external crystal oscillator is halted.
6. The PLL is halted.
7. LED indicators are disabled.
The Hub is “operational” 500
μs after RESET_N is negated.
Once operational, the Hub immediately reads OEM-specific data from the external EEPROM (if the
SMBus option is not disabled).
HUB
100K
Strap Low
LED
Pin
100K
Strap High
LED
Pin
+V
LED
LED