USB334X datasheet(55/92 Pages) MICROCHIP

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DS00002646A-page 55

USB334x

To send the ‘F0’ PID, the link will be required to use the TX CMD with NOPID to initiate the transmit and then follow up

the TX CMD with the ‘F0’ PID. The data bytes follow as in a normal transmit, in OpMode 00b. The key difference is in

that the link will have to send the PID the same as it would send a data packet. The USB334x is able to recognize the

LPM transmit and correctly send the PID information.

6.5

Low Power Mode

Low Power Mode is a power down state to save current when the USB session is suspended. The Link controls when

the PHY is placed into or out of Low Power Mode. In Low Power Mode all of the circuits are powered down except the

interface pins, Full Speed receiver, VBUS comparators, and IdGnd comparator. The VBUS and ID comparators can

optionally be powered down to save current as shown in Section 6.5.5, "Minimizing Current in Low Power Mode," on

page 58.

Before entering Low Power Mode, the USB334x must be configured to set the desired state of the USB transceiver. The

XcvrSelect[1:0], TermSelect and OpMode[1:0] bits in the Function Control register, and the DpPulldown and DmPull-

down bits in the OTG Control register control the configuration as shown in Table 5-1. The DP and DM pins are config-

ured to a high impedance state by configuring OpMode[1:0] = 01 as shown in the programming example in Table 6-8.

Pull-down resistors with a value of approximately 2MΩ are present on the DP and DM pins to avoid false linestate indi-

cations that could result if the pins were allowed to float.

6.5.1

ENTERING LOW POWER/SUSPEND MODE

To enter Low Power Mode, the Link will write a 0 or clear the SuspendM bit in the Function Control register. After this

write is complete, the PHY will assert DIR high and after a minimum of five rising edges of CLKOUT, drive the clock low.

After the clock is stopped, the PHY will enter a low power state to conserve current. Placing the PHY in Suspend Mode

is not related to USB Suspend. To clarify this point, USB Suspend is initiated when a USB host stops data transmissions

and enters Full-Speed mode with 15KΩ pull-down resistors on DP and DM. The suspended device goes to Full-Speed

mode with a pull-up on DP. Both the host and device remain in this state until one of them drives DM high (this is called

a resume).

FIGURE 6-10:

LPM TOKEN TRANSMIT

DATA[7:0]

DP/DM

DIR

CLK

STP

NXT

TXD CMD

(40h TX NOPID )

Idle

PID

(F0h)

IDLE

SE0

!SQUELCH

SE0

Turn

Around

RXD

CMD

Turn

Around

IDLE

USB334X 数据表(PDF) 55 Page - Microchip Technology

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