SMSC USB2524 - Manual (Page 47)

USB MultiSwitch TM Hub
Datasheet
SMSC USB2524 47 Revision 1.91 (08-22-07)
DATASHEET
Chapter 9 Reset
9.1 Reset
There are two different resets that the Hub experiences. One is a hardware reset (via the RESET_N
pin) and the second is a USB Bus Reset.
9.1.1 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 (300μA for the
Hub and 200
μA for the external circuitry).
Assertion of RESET_N (external pin) causes the following:
„ All downstream ports are disabled, and PRTPWR power to downstream devices is removed.
„ The PHYs are disabled, and the differential pairs will be in a high-impedance state.
„ All transactions immediately terminate; no states are saved.
„ All internal registers return to the default state (in most cases, 00(h)).
„ The external crystal oscillator is halted.
„ The PLL is halted.
„ 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) or the internal ROM.