Universal Serial Bus (USB)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
31-6
Freescale Semiconductor
Figure 31-3. USB Controller Operating Modes
Table 31-2. USB Tokens
Token
Description
OUT
Reception begins when an OUT token is received. The USB controller fetches the next BD associated
with the endpoint; if the BD is empty, the controller starts sending the incoming packet to the buffer. After
the buffer is full, the USB controller clears RxBD[E] and generates an interrupt if RxBD[I] = 1. If the
incoming packet is larger than the buffer, the USB controller fetches the next BD, and, if it is empty, sends
the rest of the packet to its buffer. The entire packet, including the DATA0/DATA1 PID, is written to the
receive buffers. Software must check data packet synchronization by monitoring the DATA0/DATA1 PID
sequence toggle.
If the packet reception has no CRC or bit stuff errors, the USB receiver sends the handshake selected
in the endpoint configuration register USEP
n[RHS] (see table below) to the host. If an error occurs, no
handshake packet is returned and error status bits are set in the last RxBD associated with this packet.
USB Out Token Reception
USEP
n[RHS]
Data Packet Corrupted
Handshake Sent to Host
xx
Yes
None (Data Discarded)
00 (Normal)
No
ACK
01 (Ignore)
No
None
10 (NAK)
No
NAK
11 (STALL)
No
STALL
reset
unenumerated
IDLE
setup
transmit
receive
start of frame
SETUP
token
IN
token
OUT
token
SOF
token
Enumeration
process
Summary of Contents for PowerQUICC MPC870
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