FW82801DBM S L6DN Intel, FW82801DBM S L6DN Datasheet - Page 198

• Manufacturer Part Number: FW82801DBM S L6DN
• Manufacturer: Intel

Specifications of FW82801DBM S L6DN

• Lead Free Status / RoHS Status: Not Compliant

Functional Description
5.16.3
5.16.4
5.16.4.1
5.16.4.2
5.16.4.3
198
Figure 5-18. 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 1 is represented by no change in level and a 0 is represented by a change in
level. A string of 0s causes the NRZI data to toggle each bit time. A string of 1s 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 0 is inserted after every six consecutive
1s 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
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
NRZI Data
CLOCK
Data
Intel
®
Figure
82801DBM ICH4-M Datasheet
5-18.