Universal Serial Bus (USB)
12 - 20 TMS320F2837xD Microcontroller Workshop - Communications
USB Communication
USB Communication
A component on the bus is either a…
Host (the master)
Device (the slave) – also known as peripheral or
function
Hub (neither master nor slave; allows for expansion)
Communication model is heavily master/slave
As opposed to peer-to-peer/networking (i.e. 1394/Firewire)
Master runs the entire bus
Only the master keeps track of other devices on bus
Only the master can initiate transactions
Slave simply responds to host commands
This makes USB simpler, and cheaper to
implement
Enumeration
Enumeration
USB is universal because of Enumeration
Process in which a Host attempts to identify a Device
If no device attached to a downstream port,
then the port sees Hi-Z
When full-speed device is attached, it pulls up
D+ line
When the Host see a Device, it polls for
descriptor information
Essentially asking, “what are you?”
Descriptors contain information the host can
use to identify a driver
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