ST72734 datasheet(79/144 Pages) STMICROELECTRONICS

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ST72774/ST727754/ST72734

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4.6 USB INTERFACE (USB)

4.6.1 Introduction

The USB Interface implements a low-speed

function interface between the USB and the ST7

microcontroller. It is a highly integrated circuit

which

includes

the

transceiver,

3.3

voltage

regulator, SIE and DMA. No external components

are needed apart from the external pull-up on

USBDM for low speed recognition by the USB

host.

4.6.2 Main Features

USB Specification Version 1.0 Compliant

Supports Low-Speed USB Protocol

Two or Three Endpoints (including default one)

depending on the device (see device feature list

and register map)

CRC

generation/checking,

NRZI

encoding/

decoding and bit-stuffing

USB Suspend/Resume operations

DMA Data transfers

On-Chip 3.3V Regulator

On-Chip USB Transceiver

4.6.3 Functional Description

The block diagram in Figure 50, 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

transmission/reception,

and

handshaking

required by the USB standard. It also performs

frame formatting, including CRC generation and

checking.

Endpoints

The

Endpoint

registers

indicate

the

microcontroller is ready to transmit/receive, and

how many bytes need to be transmitted.

DMA

When a token for a valid Endpoint is recognized by

the USB interface, the related data transfer takes

place, using DMA. At the end of the transaction, an

interrupt is generated.

Interrupts

reading

the

Interrupt

Status

application software can know which USB event

has occurred.

Figure 50. USB block diagram

CPU

MEMORY

Transceiver

3.3V

Voltage

Regulator

SIE

ENDPOINT

DMA

INTERRUPT

Address,

and interrupts

USBDM

USBDP

USBVCC

6 MHz

REGISTERS

data busses

USBGND

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