Software – General Concepts

The General USB Process

The Enumeration Process:What happens when a device is connected?

5.The available bandwidth is then divided into frames, and the host controls those frames which contain 1,500 bytes. Every millisecond a new frame begins. Within the frame, slots are reserved for isochronous and interrupt devices (up to 90%) so that they are guaranteed the bandwidth they need. Bulk and control transfers use whatever space is left.

 

 

 

 

 

 

 

 

 

 

TM

 

 

 

 

 

 

 

Frame

 

 

 

 

 

 

Transfer 1

 

 

 

Transfer 2

 

 

 

Transfer 3

Transaction

Transaction 1

Transaction 2

Transaction 3

Transaction 1

Start of Frame

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

 

 

 

 

1500 bytes / 1 Ms

 

 

 

 

 

 

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Image 109
Freescale Semiconductor TWR-MCF52259-Ethenet manual Frame