USB3370 datasheet(49/75 Pages) MICROCHIP

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DS00001915B-page 49

USB3370

Exiting Carkit Mode is the same as exiting Low Power Mode as described in Section 6.5.2. The Link must assert STP

to signal the PHY to exit serial mode. When the PHY can accept a command, DIR is de-asserted and the PHY will wait

until the Link de-asserts STP to resume synchronous ULPI operation. The RESETB pin can also be pulsed low to reset

the USB3370 and return it to Synchronous Mode.

6.7.1

ENTERING USB UART MODE

The USB3370 can be placed into UART Mode by first setting the TxdEn and RxdEn bits in the Carkit Control register.

Then the Link can set the CarkitMode bit in the Interface Control register. The TxdEn and RxdEn bits must be written

before the CarkitMode bit.

After the CarkitMode bit is set, the ULPI interface will become redefined as described in Table 6-10, and the USB3370

will transmit data through the DATA[0] to DM of the USB connector and receive data on DP and pass the information

the Link on DATA[1].

When entering UART mode, the regulator output will automatically switch to the value configured by the UART RegOut-

put bits in the

USB IO & Power Management register and the RCD pull-up resistors will be applied internally to DP and

. This will hold the UART in its default operating state.

While in UART mode, the transmit edge rates can be set to either the Full Speed USB or Low Speed USB edge rates

by using the XcvrSelect[1:0] bits in the Function Control register.

6.8

RID Converter Operation

The RID converter is designed to read the value of the ID resistance to ground and report back its value through the

ULPI interface.

When a resistor to ground is applied to the ID pin the state of the IdGnd comparator will change from a 1 to a 0 as

described in Section 5.7.1. If the USB3370 is in ULPI mode, an RXCMD will be generated with bit 6 low. If the USB3370

is in Low Power Mode (or one of the other non-ULPI modes), the DATA[3] interrupt signal will go high.

After the USB3370 has detected the change of state on the ID pin, the RID converter can be used to determine the value

of ID resistance. To start a ID resistance measurement, the RidConversionStart bit is set in the Vendor Rid Conversion

TABLE 6-10:

PIN DEFINITIONS IN CARKIT MODE

Signal

Connected To

Direction

Description

txd

DATA[0]

UART TXD signal that is routed to the DM pin if the TxdEn

is set in the Carkit Control register.

rxd

DATA[1]

OUT

UART RXD signal that is routed to the DP pin if the RxdEn

bit is set in the Carkit Control register.

reserved

DATA[2]

OUT

Driven Low (CarkitDataMC = 0, default)

Tri-state (CarkitDataMC = 1)

int

DATA[3]

OUT

Asserted when any unmasked interrupt occurs. Active high.

reserved

DATA[4:7]

OUT

Driven Low.

TABLE 6-11:

ULPI REGISTER PROGRAMMING EXAMPLE TO ENTER UART MODE

R/W

Address

(HEX)

Value

(HEX)

Description

Result

Configure Non-Driving mode

Select FS transmit edge rates

OpMode

=01

XcvrSelect

=01

Set regulator to 3.3V

UART RegOutput

=00

Enable UART connections

RxdEn

TxdEn

Enable carkit mode

CarkitMode

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