adm6996f Infineon Technologies Corporation, adm6996f Datasheet - Page 21

• Manufacturer Part Number: adm6996f
• Description: 6 Port 10/100 Mb/s Single Chip Ethernet Switch Controller
• Manufacturer: Infineon Technologies Corporation

ADM6996F
Infineon-ADMtek Co Ltd.
3.4.4 Data De-scrambling
3.4.5 Symbol Alignment
3.4.6 Symbol Decoding
3.4.7 Valid Data Signal
The de-scrambler acquires synchronization with the data stream by recognizing idle
bursts of 40 or more bits and locking its deciphering Linear Feedback Shift Register
(LFSR) to the state of the scrambling LFSR. Upon achieving synchronization, the
incoming data is XORed by the deciphering LFSR and de-scrambled.
In order to maintain synchronization, the de-scrambler continuously monitors the validity
of the unscrambled data that it generates. To ensure this, a link state monitor and a hold
timer are used to constantly monitor the synchronization status. Upon synchronization of
the de-scrambler the hold timer starts a 722 us countdown. Upon detection of sufficient
idle symbols within the 722 us period, the hold timer will reset and begin a new
countdown. This monitoring operation will continue indefinitely given a properly
operating network connection with good signal integrity. If the link state monitor does
not recognize sufficient unscrambled idle symbols within 722 us period, the de-scrambler
will be forced out of the current state of synchronization and reset in order to re-acquire
synchronization.
The symbol alignment circuit in the ADM6996F determines code word alignment by
recognizing the /J/K delimiter pair. This circuit operates on unaligned data from the de-
scrambler. Once the /J/K symbol pair (11000 10001) is detected, subsequent data is
aligned on a fixed boundary.
The symbol decoder functions as a look-up table that translates incoming 5B symbols
into 4B nibbles as shown in Table 1. The symbol decoder first detects the /J/K symbol
pair preceded by idle symbols and replaces the symbol with MAC preamble. All
subsequent 5B symbols are converted to the corresponding 4B nibbles for the duration of
the entire packet. This conversion ceases upon the detection of the /T/R symbol pair
denoting the end of stream delimiter (ESD). The translated data is presented on the
internal RXD[3:0] signal lines with RXD[0] represents the least significant bit of the
translated nibble.
The valid data signal (RXDV) indicates that recovered and decoded nibbles are being
presented on the internal RXD[3:0] synchronous to receive clock, RXCLK. RXDV is
asserted when the first nibble of translated /J/K is ready for transfer over the internal MII.
It remains active until either the /T/R delimiter is recognized, link test indicates failure, or
no signal is detected. On any of these conditions, RXDV is de-asserted.
Function Description
3-3