USB333X datasheet(32/85 Pages) MICROCHIP

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USB333x

DS00001880A-page 32

 2009 - 2015 Microchip Technology Inc.

5.6.1.1

USB OTG Operation

The USB333x 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 USB333x 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 USB333x 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 5.6.1.2.

5.6.1.2

Measuring ID Resistance to Ground

The Link can use the integrated resistance measurement capabilities of the USB333x to determine the value of an ID

resistance to ground. Table 5-5 details the values of resistance to ground that the USB333x can detect.

FIGURE 5-9:

USB333X ID RESISTOR DETECTION CIRCUITRY

TABLE 5-5:

VALID VALUES OF ID RESISTANCE TO GROUND

ID Resistance to Ground

RID Value

Ground

000

75Ω +/-1%

001

102kΩ +/-1%

010

200kΩ+/-1%

011

Floating

101

Note:

IdPullUp = 0

IdPullup

IdGnd

Vref IdGnd

IdFloat

OTG Module

VDD33

To USB Con.

RidValue

Vref IdFloat

IdGnd Rise

IdGnd Fall

IdFloatRise

IdFloatFall

Rid ADC

IdGndDrv

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