ST7SCR datasheet(44/102 Pages) STMICROELECTRONICS

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ST7SCR

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12.3 USB INTERFACE (USB)

12.3.1 Introduction

The USB Interface implements a full-speed func-

tion interface between the USB and the ST7 mi-

crocontroller. It is a highly integrated circuit which

includes the transceiver, 3.3 voltage regulator, SIE

and USB Data Buffer interface. No external com-

ponents are needed apart from the external pull-

up on USBDP for full speed recognition by the

USB host.

12.3.2 Main Features

USB Specification Version 1.1 Compliant

Supports Full-Speed USB Protocol

Seven Endpoints (including default endpoint)

CRC

generation/checking,

NRZI

encoding/

decoding and bit-stuffing

USB Suspend/Resume operations

On-Chip 3.3V Regulator

On-Chip USB Transceiver

12.3.3 Functional Description

The block diagram in Figure 27, gives an overview

of the USB interface hardware.

For general information on the USB, refer to the

“Universal Serial Bus Specifications” document

available at http//:www.usb.org.

Serial Interface Engine

The SIE (Serial Interface Engine) interfaces with

the USB, via the transceiver.

The SIE processes tokens, handles data transmis-

sion/reception, and handshaking as required by

the USB standard. It also performs frame format-

ting, including CRC generation and checking.

Endpoints

The Endpoint registers indicate if the microcontrol-

ler is ready to transmit/receive, and how many

bytes need to be transmitted.

Data Transfer to/from USB Data Buffer Memory

When a token for a valid Endpoint is recognized by

the USB interface, the related data transfer takes

place to/from the USB data buffer. At the end of

the transaction, an interrupt is generated.

Interrupts

By reading the Interrupt Status register, applica-

tion software can know which USB event has oc-

curred.

Figure 27. USB Block Diagram

CPU

Transceiver

3.3V

Voltage

Regulator

SIE

ENDPOINT

BUFFER

USB

Address,

and interrupts

USBDM

USBDP

USBVCC

48 MHz

REGISTERS

data busses

USBGND

BUFFER

USB

DATA

INTERFACE

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