EP80579 Datasheet, PDF (971/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
25.8.3.1
Packet Identifier Field
A packet identifier (PID) immediately follows the SYNC field of every USB packet. A PID
consists of a four bit packet type field followed by a four-bit check field . The PID
indicates the type of packet and, by inference, the format of the packet and the type of
error detection applied to the packet. The four-bit check field of the PID insures reliable
decoding of the PID so that the remainder of the packet is interpreted correctly. The
PID check field is generated by performing a ones complement of the packet type field.
Any PID received with a failed check field or which decodes to a non-defined value is
assumed to be corrupted and it, as well as the remainder of the packet, is ignored by
the receiver.
PIDs are divided into four coding groups: token, data, handshake, and special, with the
first two transmitted PID bits (PID<1:0>) indicating which group. This accounts for the
distribution of PID codes.
25.8.4
Address Fields
Function endpoints are addressed using two fields: the function address field and the
endpoint field. Full details on this are given in the USB Specification.
25.8.4.1
Address Field
The function address (ADDR) field specifies the function, via its address, that is either
the source or destination of a data packet, depending on the value of the token PID. A
total of 128 addresses are specified as ADDR[6:0]. The ADDR field is specified for IN,
SETUP, and OUT tokens.
25.8.4.2
Endpoint Field
An additional four-bit endpoint (ENDP) field, permits more flexible addressing of
functions in which more than one sub-channel is required. Endpoint numbers are
function specific. The endpoint field is defined for IN, SETUP, and OUT token PIDs only.
25.8.5
Frame Number Field
The frame number field is an 11-bit field that increments by the host on a per frame
basis. The frame number field rolls over upon reaching its maximum value of x7FF, and
is sent only for SOF tokens at the start of each frame.
25.8.6
Data Field
The data field may range from 0 to 1023 bytes and must be an integral numbers of
bytes. Table 25-31 lists the format for multiple bytes. Data bits within each byte are
shifted out LSB first.
Table 25-31. Data Field
Bit
x-1
x
x+1
x+2
x+3
x+4
Data Sent
Byte N - 1, D7
Byte N, D0
Byte N, D1
Byte N, D2
Byte N, D3
Byte N, D4
August 2009
Order Number: 320066-003US
Intel^® EP80579 Integrated Processor Product Line Datasheet
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