USB3370 datasheet(25/75 Pages) MICROCHIP

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DS00001915B-page 25

USB3370

5.7.1.2

Measuring ID Resistance to Ground

The Link can use the integrated resistance measurement capabilities of the USB3370 to determine the value of an ID

resistance to ground. The following table details the valid values of resistance to ground that the USB3370 can detect.

The ID resistance to ground can be read while the USB3370 is in Synchronous Mode. When a resistor to ground is

attached to the ID pin, the state of the IdGnd comparator will change. After the Link has detected ID transition to ground,

it can use the methods described in Section 6.8 to operate the Rid converter.

5.7.1.3

Using IdFloat Comparator (not recommended).

The ID pin can be either grounded, floated, or connected to ground with a 102kΩ external resistor. To detect the 102K

resistor, set the idPullup bit in the OTG Control register, causing the USB3370 to apply the 100K internal pull-up con-

nected between the ID pin and VDD33. Set the idFloatRise and idFloatFall bits in the Carkit Interrupt Enable register to

enable the IdFloat comparator to generate an RXCMD to the Link when the state of the IdFloat changes. As described

in Figure 6-3, the alt_int bit of the RXCMD will be set. The values of IdGnd and IdFloat are shown for the three types

cables that can attach to the USB Connector in Table 5-3.

To save current when an A Plug is inserted, the internal 102kΩ pull-up resistor can be disabled by clearing the IdPullUp

bit in the OTG Control register and the IdFloatRise and IdFloatFall bits in both the USB Interrupt Enable Rising and USB

Interrupt Enable Falling registers. If the cable is removed the weak RIDW will pull the ID pin high.

The IdGnd value can be read using the ULPI USB Interrupt Status register, bit 4. In host mode, it can be set to generate

an interrupt when IdGnd changes by setting the appropriate bits in the USB Interrupt Enable Rising and USB Interrupt

Enable Falling registers. The IdFloat value can be read by reading the ULPI Carkit Interrupt Status register bit 0.

FIGURE 5-7:

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

Note:

The ULPI specification details a method to detect a 102kΩ resistance to ground using the IdFloat compar-

ator. This method can only detect 0ohms, 102kΩ, and floating terminations of the ID pin. Due to this limita-

tion it is recommended to use the RID Converter as described in Section 5.7.1.2.

TABLE 5-3:

IDGND AND IDFLOAT VS. ID RESISTANCE TO GROUND

ID Resistance

IDGND

IDFLOAT

Float

102K

GND

Note:

The ULPI register bits IdPullUp, IdFloatRise, and IdFloatFall should be enabled.

Note:

The IdGnd switch has been provided to ground the ID pin for future applications.

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