FW82801DB S L66K Intel, FW82801DB S L66K Datasheet - Page 184

• Manufacturer Part Number: FW82801DB S L66K
• Manufacturer: Intel

Specifications of FW82801DB S L66K

• Lead Free Status / RoHS Status: Supplier Unconfirmed

Functional Description
5.16.3
5.16.4
5.16.4.1
5.16.4.2
5.16.4.3
184
Figure 5-17. USB Data Encoding
Data Encoding and Bit Stuffing
The USB employs NRZI data encoding (Non-Return to Zero Inverted) when transmitting packets.
In NRZI encoding; a one is represented by no change in level, and a zero is represented by a change
in level. A string of zeros causes the NRZI data to toggle each bit time. A string of ones causes long
periods with no transitions in the data. To ensure adequate signal transitions, bit stuffing is
employed by the transmitting device when sending a packet on the USB. A zero is inserted after
every six, consecutive ones in the data stream before the data is NRZI encoded to force a transition
in the NRZI data stream. This gives the receiver logic a data transition at least once every seven bit
times to guarantee the data and clock lock. A waveform of the data encoding is shown in
Figure
Bit stuffing is enabled beginning with the Sync Pattern and throughout the entire transmission. The
data “one” that ends the Sync Pattern is counted as the first one in a sequence. Bit stuffing is always
enforced, without exception. If required by the bit stuffing rules, a zero bit will be inserted even if
it is the last bit before the end-of-packet (EOP) signal.
Bus Protocol
Bit Ordering
Bits are sent out onto the bus least significant bit (LSb) first, followed by next LSb, through to the
most significant bit (MSb) last.
SYNC Field
All packets begin with a synchronization (SYNC) field, which is a coded sequence that generates a
maximum edge transition density. The SYNC field appears on the bus as IDLE followed by the
binary string “KJKJKJKK,” in its NRZI encoding. It is used by the input circuitry to align
incoming data with the local clock and is defined to be eight bits in length. SYNC serves only as a
synchronization mechanism and is not shown in the following packet diagrams. The last two bits in
the SYNC field are a marker that is used to identify the first bit of the PID. All subsequent bits in
the packet must be indexed from this point.
Packet Field Formats
Field formats for the token, data, and handshake packets are described in the following section. The
effects of NRZI coding and bit stuffing have been removed for the sake of clarity. All packets have
distinct start and end of packet delimiters.
Bit Stuffed Data
5-17.
NRZI Data
CLOCK
Data
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82801DB ICH4 Datasheet