Patent ID: 7193442

Claim:
An apparatus for a USB 1.1 device including a microcontroller for implementing USB OTG functions comprising: a Vbus pulsing detect circuit controlled by the microcontroller including a PMOS transistor ( 506 ) having a source connected to a power supply, a drain, and a gate connected to a charge-discharge control output of the microcontroller ( 500 ), a first resistor ( 504 ) connected between the source and gate of said PMOS transistor ( 506 ), a capacitor ( 512 ) connected between said drain of said PMOS transistor ( 506 ) and ground, a second resistor ( 507 ) having a first terminal connected to said drain of said PMOS transistor ( 506 ), and a second terminal, an NMOS transistor ( 508 ) having a source connected to said second terminal of said second resistor ( 507 ), a drain connected to ground, and a gate, a third resistor ( 505 ) connected between the charge-discharge control output of the microcontroller ( 500 ) and said gate of said NMOS transistor ( 508 ), a fourth resistor ( 509 ) connected between said gate of said NMOS transistor ( 508 ) and ground, and a comparator ( 511 ) having a first input connected to said drain of said PMOS transistor ( 506 ), a second input receiving the Vbus ( 501 ), and an output ( 503 ) connected to a Vbus detect input of the microcontroller; said microcontroller programmed to correlate a time between sending a signal on the charge-discharge control output of the microcontroller ( 500 ) to turn said NMOS transistor ( 508 ) ON and detection of tripping of said comparator ( 511 ) to a voltage on the Vbus ( 501 ) corresponding to a discharge time determined by a capacitance of said capacitor ( 512 ) and a resistance of said second resistor ( 507 ); a Vbus pulsing circuit controlled by the microcontroller; and a data line pull down detect circuit controlled by the microcontroller.