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| PIC18F2450_08 Datasheet, PDF (131/324 Pages) Microchip Technology – 28/40/44-Pin, High-Performance, 12 MIPS, Enhanced Flash, USB Microcontrollers with nanoWatt Technology | |||
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PIC18F2450/4450
14.0 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 is provided in Section 14.9 âOverview of
USBâ only for application design reference. Designers
are encouraged to refer to the official specification
published by the USB Implementers 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.
14.1 Overview of the USB Peripheral
The PIC18F2450/4450 device family contains a full-
speed and low-speed, compatible USB Serial Interface
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
deviceâs 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
endpoint memory usage within the USB RAM space.
Figure 14-1 presents a general overview of the USB
peripheral and its features.
FIGURE 14-1:
USB PERIPHERAL AND OPTIONS
PIC18F2450/4450 Family
VREGEN
3.3V Regulator
EN
USB Clock from the
Oscillator Module
FSEN
UPUEN
UTRDIS
P
P
Internal Pull-ups
Transceiver
FS
OE
USB Control and
Configuration
USB
SIE
VUSB
External 3.3V
Supply(3)
External
Pull-ups(2)
(Full
Speed)
(Low
Speed)
D+
D-
UOE(1)
VM(1)
VP(1)
RCV(1)
VMO(1)
VPO(1)
External
Transceiver
USB Bus
USB Bus
256-Byte
USB RAM
Note 1: This signal is only available if the internal transceiver is disabled (UTRDIS = 1).
2: The pull-ups can be supplied either from the VUSB pin or from an external 3.3V supply.
3: Do not enable the internal regulator when using an external 3.3V supply.
© 2008 Microchip Technology Inc.
DS39760D-page 129
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