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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
155 of 571
NXP Semiconductors
UM10316
Chapter 13: LPC29xx USB device
5.1 Analog transceiver
The USB Device Controller has a built-in analog transceiver (ATX). The USB ATX
sends/receives the bi-directional D+ and D- signals of the USB bus.
5.2 Serial Interface Engine (SIE)
The SIE implements the full USB protocol layer. It is completely hardwired for speed and
needs no firmware intervention. It handles transfer of data between the endpoint buffers in
EP_RAM and the USB bus. The functions of this block include: synchronization pattern
recognition, parallel/serial conversion, bit stuffing/de-stuffing, CRC checking/generation,
PID verification/generation, address recognition, and handshake evaluation/generation.
5.3 Endpoint RAM (EP_RAM)
Each endpoint buffer is implemented as an SRAM based FIFO. The SRAM dedicated for
this purpose is called the EP_RAM. Each realized endpoint has a reserved space in the
EP_RAM. The total EP_RAM space required depends on the number of realized
endpoints, the maximum packet size of the endpoint, and whether the endpoint supports
double buffering.
5.4 EP_RAM access control
The EP_RAM Access Control logic handles transfer of data from/to the EP_RAM and the
three sources that can access it: the CPU (via the Register Interface), the SIE, and the
DMA Engine.
5.5 DMA engine and bus master interface
When enabled for an endpoint, the DMA Engine transfers data between RAM on the AHB
bus and the endpoint’s buffer in EP_RAM. A single DMA channel is shared between all
endpoints. When transferring data, the DMA Engine functions as a master on the AHB
bus through the bus master interface.
5.6 Register interface
The Register Interface allows the CPU to control the operation of the USB Device
Controller. It also provides a way to write transmit data to the controller and read receive
data from the controller.
5.7 SoftConnect
The connection to the USB is accomplished by bringing D+ (for a full-speed device) HIGH
through a 1.5 kOhm pull-up resistor. The SoftConnect feature can be used to allow
software to finish its initialization sequence before deciding to establish connection to the
USB. Re-initialization of the USB bus connection can also be performed without having to
unplug the cable.
To use the SoftConnect feature, the CONNECT signal should control an external switch
that connects the 1.5 kOhm resistor between D+ and +3.3V. Software can then control the
CONNECT signal by writing to the CON bit using the SIE Set Device Status command.