USB334X datasheet(36/92 Pages) MICROCHIP

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USB334x

DS00002646A-page 36

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The SessEnd Comparator is only used when configured as an OTG device. If the USB334x is used as a Host or Device

only the SessEnd Comparator should be disabled, using the method described above.

5.7.2.2

SessVld Comparator

The SessVld comparator is used when the PHY is configured as both an A and B device. When configured as an A

device, the SessVld is used to detect Session Request protocol (SRP). When configured as a B device, SessVld is used

to detect the presence of VBUS. The SessVld comparator output can also be read from the USB Interrupt Status regis-

ter. The SessVld comparator will also generate an RX CMD, as detailed in Section 6.3.1, "ULPI Receive Command (RX

CMD)," on page 48, anytime the comparator changes state. The SessVld interrupts can be disabled by clearing this bit

in both the USB Interrupt Enable Rising and USB Interrupt Enable Falling registers. When the interrupts are disabled,

the SessVld comparator is still operational and will generate RX CMD’s. The SessVld comparator trip point is detailed

in Table 4-9.

5.7.2.3

VbusVld Comparator

The VbusVld comparator is only used when the USB334x is configured as a host that can supply less than 100mA VBUS

current. In the USB protocol, the A-device supplies the VBUS voltage and is responsible to ensure it remains within a

specified voltage range. The VbusVld comparator can be disabled by clearing this bit in both the USB Interrupt Enable

Rising and USB Interrupt Enable Falling registers. When disabled, bit 1 of the USB Interrupt Status register will return

a 0. The VbusVld comparator threshold values are detailed in Table 4-9.

If the USB334x is used as a Device only the VbusValid Comparator should be disabled, using the method described

above.

The USB334x includes the external VbusVld indicator logic as detailed in the ULPI Specification. The external VbusVld

indicator is tied to a logic one. The decoding of this logic is shown in Table 5-5 below. By default this logic is disabled.

Note 5-5

A peripheral should not use VbusVld to begin operation. The peripheral should use SessVld to detect

the presence of VBUS on the USB connector. VbusVld should only be used for USB Host and OTG

A-device applications.

Note:

The OTG Supplement specifies a voltage range for A-Device Session Valid and B-Device Session Valid

comparator. The USB334x PHY combines the two comparators into one and uses the narrower threshold

range.

TABLE 5-5:

EXTERNAL VBUS INDICATOR LOGIC

Typical

Application

Use External

Vbus

Indicator

Pass Thru

Indicator

Complement

RXCMD Vbus Valid

Encoding Source

OTG Device

Internal VbusVld comparator (Default)

Fixed 1

Fixed 0

Internal VbusVld comparator.

Fixed 0

Standard Host

Fixed 1

Fixed 0

Standard

Peripheral

Internal VbusVld comparator. This

information should not be used by the

Link. (Note 5-5)

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