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2009 Microchip Technology Inc.

DS39632E-page 165

PIC18F2455/2550/4455/4550

17.0 UNIVERSAL SERIAL BUS

(USB)

This section describes the details of the USB

peripheral. Because of the very specific nature of the

module, knowledge of USB is expected. Some

high-level

USB

information

provided

Section 17.10 “Overview of USB” only for application

design reference. Designers are encouraged to refer to

the official specification published by the USB Imple-

menters Forum (USB-IF) for the latest information.

USB specification Revision 2.0 is the most current

specification at the time of publication of this document.

17.1

Overview of the USB Peripheral

The PIC18FX455/X550 device family contains a

full-speed and low-speed compatible USB Serial Inter-

face Engine (SIE) that allows fast communication

between any USB host and the PIC microcontroller.

The SIE can be interfaced directly to the USB, utilizing

the internal transceiver, or it can be connected through

an external transceiver. An internal 3.3V regulator is

also available to power the internal transceiver in 5V

applications.

Some special hardware features have been included to

improve performance. Dual port memory in the

device’s data memory space (USB RAM) has been

supplied to share direct memory access between the

microcontroller core and the SIE. Buffer descriptors are

also provided, allowing users to freely program end-

point memory usage within the USB RAM space. A

Streaming Parallel Port has been provided to support

the uninterrupted transfer of large volumes of data,

such as isochronous data, to external memory buffers.

Figure 17-1 presents a general overview of the USB

peripheral and its features.

FIGURE 17-1:

USB PERIPHERAL AND OPTIONS

UOE(1)

1Kbyte

USB RAM

USB

SIE

USB Control and

VM(1)

VP(1)

RCV(1)

VMO(1)

VPO(1)

Transceiver

External

Transceiver

3.3V Regulator

D+

D-

Internal Pull-ups

UOE

VUSB

External 3.3V

Supply(3)

FSEN

UPUEN

UTRDIS

USB Clock from the

Oscillator Module

VREGEN

Optional

External

Pull-ups(2)

(Low

(Full

PIC18FX455/X550 Family

SPP7:SPP0

USB Bus

Speed)

Note 1: This signal is only available if the internal transceiver is disabled (UTRDIS = 1).

2: The internal pull-up resistors should be disabled (UPUEN = 0) if external pull-up resistors are used.

3: Do not enable the internal regulator when using an external 3.3V supply.

Configuration

CK1SPP

CK2SPP

CSSPP

OESPP

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