Sending And Receiving - Freescale Semiconductor MPC850 User Manual

32.5 Sending and Receiving

After reset, the USB slave controller is addressable at the USB default address (0x00). The
external host assigns a unique address (other than 0x00) to the controller during
enumeration. Software should program the USB slave address register (USADR) with the
assigned address.
The USB endpoint configuration registers (USEPn) are used to configure each of the four
independent endpoints to support either control, interrupt, bulk, or isochronous transfers.
Note that the USB system software uses endpoint 0 as a control pipe, so it must be
configured for control transfer mode (USEP0[TM] = 0b00). Additional control pipes can
be provided by other endpoints.
Figure 32-3. shows the logical flow of USB controller operation.
Once enabled, the USB controller looks for valid token packets (see Table 32-2.). The
controller ignores packets that fail the PID or CRC check or that are not 3 bytes long.
Unenumerated
SETUP
Token
IN
Token
Setup
Send
Figure 32-3. USB Controller Operation Flow
Chapter 32. Universal Serial Bus Controller
Reset
Enumeration
Process
Idle
SOF
Token
OUT
Token
Receive
Sending and Receiving
SOF