Lantronix DSTni-EX Benutzerhandbuch

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USB is a serial bus operating at 12 Mb/s. USB provides an expandable, hot-pluggable Plug-
and-Play serial interface that ensures a standard, low-cost socket for adding external peripheral 
devices.  

USB allows the connection of up to 127 devices. Devices suitable for USB range from simple 
input devices such as keyboards, mice, and joysticks, to advanced devices such as printers, 
scanners, storage devices, modems, and video-conferencing cameras. 

Version 1.1 of the USB specification provides for peripheral speeds of up to 1.5 Mbps for low-
speed devices and up to 12 Mbps for full-speed devices. 

The DSTni USB interrupt is located at base input/output (I/O) of 9800h. It is logically ORed with 
external interrupt 3. 

The USB core has three functional blocks.  

 

Serial Interface Engine (SIE) 

 

Microprocessor Interface 

 

Digital Phase-Locked Loop Logic 

 

Serial Interface Engine 
The USB Serial Interface Engine (USB SIE) has two major sections: Tx Logic and Rx Logic.  

Tx Logic formats and transmits data packets that the microprocessor builds in memory. These 
packets are converted from a parallel-to-serial data stream. Tx Logic performs all the necessary 
USB data formatting, including: 

 

NRZI encoding 

 

Bit-stuff 

 

Cyclic Redundancy Check (CRC) computation 

 

Addition of SYNC field and EOP 

The Rx Logic receives USB data and stores the packets in memory so the microprocessor can 
process them. Serial USB data converts to a byte-wide parallel data stream and is stored in 
system memory. The receive logic:  

 

Decodes an NRZ USB serial data stream 

 

Performs bit-stuff removal 

 

Performs CRC check, PID check, and other USB protocol-layer checks