Rev. 3.0, 03/01, page 297 of 390
5) Data Packet
The data packet contains the actual data transfer between the host and endpoint specified in the
token packet. DATA0 and DATA1 identify the packet as a data packet. The 0/1 tag on the PID
provides a mechanism for data synchronization from one data packet to the next to the same
endpoint.
The data packet includes the 4 bit PID, 4 bit inverted PID, 0-1023 data bytes, and a 16 bit CRC.
All fields are serially transmitted LSB and LSb first (except CRC). The number of data bytes
for an OUT is determined by the HC. The IN data byte count is tracked by the Data Buffer
Engine. The number of data bytes is irrelevant to the operation of the SIE.
Packet
Byte
Bit 7
Bit 0
0
1
2
...
N+2
N+3
N+4
N+5
Sync Pattern[7:0]
~PID[3:0]
High-Z
Idle
SE0
PID[3:0]
Data0[7:0]
...
DataN[7:0]
~CRC[8:15]
~CRC[0:7]
Figure 18.10 Data Packet Format
6) Handshake Packet
The handshake packet is used to close the bus transaction and report completion status. An
ACK handshake concludes a successful transaction. The STALL handshake is returned when
the device is unable to handle data due to an internal error. NAK is used when the endpoint has
no data to send or does want any data. The host can only send an ACK handshake to the device,
but the device can return any handshake. The handshake packet includes only the 4 bit PID and
4 bit inverted PID.
Packet
Byte
Bit 7
Bit 0
0
1
2
Sync Pattern[7:0]
~PID[3:0]
High-Z
Idle
SE0
PID[3:0]
Figure 18.11 Handshake Packet Format
Summary of Contents for HD64465
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