UPSD3422 datasheet(154/293 Pages) STMICROELECTRONICS

154 / 293 page

USB interface

uPSD34xx

154/293

Note:

Bits marked with a “–“ are Reserved.

25.4.1

USB device address register

Initially when a device is connected to the USB, it responds to the host on address 0. Using

the Set_Address request, the host assigns a unique address to the device. The firmware

writes this address to the USB Device Address register (see Table 70), and subsequently

the SIE only responds to transactions on that assigned address. This assigned address is in

effect until the device or an upstream hub is disconnected from the USB, the host issues a

USB Reset, or the host shuts down. The address register is cleared with a Hardware

RESET. When a USB RESET is detected, the address register should be cleared.

25.4.2

Endpoint FIFO pairing

Endpoint FIFOs can be paired for double buffering to provide an efficient method for bulk

data transfers. With double buffering enabled, the MCU can operate on one data packet

while another is being transferred over USB.

When two FIFOs are paired, the active FIFO is automatically toggled by the update of

USIZE. The MCU must only use the odd numbered endpoint FIFO when paired in order to

access the active FIFO. For example, if endpoints 3 and 4 OUT FIFOs are paired, the active

FIFO is accessed via endpoint 3’s OUT FIFO (see Table 71).

UIF3

–

NAK4F

NAK3F

NAK2F

NAK1F

NAK0F

USB IN FIFO

NAK Int. Flag

UCTL

–

USBEN

VISIBLE

WAKEUP

USB Control

USTA

–

RCVT

SETUP

OUT

USB Status

RESERVED

USEL

DIR

–

EP[2:0]

USB Endpoint

Select

UCON

–

ENABLE

STALL

TOGGL

BSY

USB Endpoint

Control

USIZE

–

SIZE[6:0]

USB FIFO

Valid Size

UBASEH

BASEADDR[15:8]

USB Base

Address High

UBASEL

BASEADDR

[7:6]

000

USB Base

Address Low

USCI

–

USCI[2:0]

USB Setup

Command

Index

USCV

USCV[7:0]

USB Setup

Command

Value

SFR

Addr

(hex)

SFR

Name

Bit Name and <Bit Address>

Reset

Value

(hex)

Comment

321

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