USB334X datasheet(33/92 Pages) MICROCHIP

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DS00002646A-page 33

USB334x

5.7.1.1

USB OTG Operation

The USB334x can detect ID grounded and ID floating to determine if an A or B cable has been inserted. The A plug will

ground the ID pin while the B plug will float the ID pin. These are the only two valid states allowed in the OTG Protocol.

To monitor the status of the ID pin, the Link activates the IdPullup bit in the OTG Control register, waits 50mS and then

reads the status of the IdGnd bit in the USB Interrupt Status register. If an A cable has been inserted the IdGnd bit will

read 0. If a B cable is inserted, the ID pin is floating and the IdGnd bit will read 1.

The USB334x provides an integrated weak pull-up resistor on the ID pin, RIDW. This resistor is present to keep the ID

pin in a known state when the IdPullup bit is disabled and the ID pin is floated. In addition to keeping the ID pin in a

known state, it enables the USB334x to generate an interrupt to inform the link when a cable with a resistor to ground

has been attached to the ID pin. The weak pull-up is small enough that the largest valid RID resistor pulls the ID pin low

and causes the IdGnd comparator to go low.

After the link has detected an ID pin state change, the RID converter can be used to determine the resistor value as

described in Section 5.7.1.2, "Measuring ID Resistance to Ground," on page 33.

5.7.1.2

Measuring ID Resistance to Ground

The Link can use the integrated resistance measurement capabilities of the USB334x to determine the value of an ID

resistance to ground. The following table details the valid values of resistance to ground that the USB334x can detect.

FIGURE 5-7:

USB334X ID RESISTOR DETECTION CIRCUITRY

IdPullup

IdGnd

Vref IdGnd

IdFloat

OTG Module

VDD33

To USB Con.

RidValue

Vref IdFloat

IdGnd Rise or

IdGnd Fall

IdFloatRise or

IdFloatFall

Rid ADC

IdGndDrv

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