BCM5208KPF Broadcom, BCM5208KPF Datasheet - Page 12

• Manufacturer Part Number: BCM5208KPF
• Manufacturer: Broadcom

Specifications of BCM5208KPF

• Number Of Receivers: 4
• Data Rate: 10/100Mbps
• Operating Temperature Classification: Commercial
• Operating Supply Voltage (min): 3.14V
• Mounting: Surface Mount
• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Lead Free Status / RoHS Status: Not Compliant

n BCM5208
MULTIMODE TRANSMIT DAC
The multimode transmit digital to analog converter (DAC) transmits MLT3-coded symbols in 100BASE-TX mode, NRZI-
coded symbols in 100BASE-FX mode, and Manchester-coded symbols in 10BASE-T mode. It performs programmable
edge-rate control in TX mode, which decreases unwanted high frequency signal components thus reducing EMI. High-
frequency pre-emphasis is performed in 10BASE-T mode; no filtering is performed in 100BASE-FX mode. The transmit
DAC utilizes a current drive output which is well balanced and produces very low noise transmit signals. PECL voltage
levels are produced with resistive terminations in 100BASE-FX mode.
STREAM CIPHER
In 100BASE-TX mode, the transmit data stream is scrambled in order to reduce radiated emissions on the twisted pair
cable. The data is scrambled by exclusive ORing the NRZ signal with the output of an 11-bit wide linear feedback shift
register (LFSR), which produces a 2047-bit non-repeating sequence. The scrambler reduces peak emissions by randomly
spreading the signal energy over the transmit frequency range, and eliminating peaks at certain frequencies. For repeater
applications, where all ports transmit the same data simultaneously, signal energy is spread further by using unique seeds
to generate a different non-repeating sequence for each of the four ports.
The receiver descrambles the incoming data stream by exclusive ORing it with the same sequence generated at the
transmitter. The descrambler detects the state of the transmit LFSR by looking for a sequence representing consecutive
idle codes. The descrambler will “lock” to the scrambler state after detecting a sufficient number of consecutive idle code-
groups. The receiver will not attempt to decode the data stream unless the descrambler is locked. Once locked, the
descrambler will continuously monitor the data stream to make sure that it has not lost synchronization. The receive data
stream is expected to contain inter-packet idle periods. If the descrambler does not detect enough idle codes within 724µs,
it will become “unlocked”, and the receive decoder will be disabled. The descrambler will always be forced into the
“unlocked” state when a link failure condition is detected.
Stream cipher scrambling/descrambling is not used in 100BASE-FX and 10BASE-T modes.
Page 4
ERROR TYPE
Stream cipher error - descrambler lost lock
Link failure
Premature end of stream
Invalid code
Transmit error
False carrier sense
V
V
V
V
V
V
V
V
V
V
* Treated as invalid code (mapped to 0111) when received in data field.
0111
0111
0111
0111
0111
0111
0111
0111
0111
0111
Table 1: 4B5B Encoding(Continued)
00000
00001
00010
00011
00101
00110
01000
01100
10000
11001
Table 2: Receive Error Encoding
B r o a d c o m C o r p o r a t i o n
Invalid Code
Invalid Code
Invalid Code
Invalid Code
Invalid Code
Invalid Code
Invalid Code
Invalid Code
Invalid Code
Invalid Code
RXD[3:0]
0010
0011
0110
0111
1000
1110
Document 5208-DS03-R¥¥¥¥¥
November 3, 1999