10
ICS1890
100Base-TX Physical Coding Sublayer [PCS]
Carrier Detector & Framer
The carrier detector examines the serial bit stream looking for
the SSD, the JK symbol pair. In the idle state, IDLE symbols
(all logic ones) will be received. If the carrier detector detects a
logic zero in the bit stream, it examines the following bits
looking for the first two non-contiguous zeros, confirms that
the first 5-bits form the J symbol (11000) and asserts carrier
detect. At this point the serial data is framed and the second
symbol is checked to confirm the K symbol (10001). If
successful, the following framed data (symbols) are presented
to the 4B5B decoder. If the JK pair is not confirmed, the false
carrier detect is asserted and the idle state is re-entered.
Collision Detector
Collision is asserted in half-duplex
mode when transmission and data reception occur
simultaneously. In full duplex mode, collision is never asserted.
Parallel/Serial Converter
This block converts data between 5-bit symbols and 1-bit
serial data.
4B/5B Encoder/Decoder
When the
ICS1890
is operating in the 100Base-TX mode,
4B5B coding is used. This coding scheme maps a 4-bit nibble
to a 5-bit code group. Since this gives 32 possible symbols
and the data only requires 16 symbols, 16 symbols are designated
control or invalid. The control symbols used are JK as the
start-of-stream delimiter (SSD), TR as the end-of-stream
delimiter (ESD), I as the IDLE symbol and H to signal an
error. All other symbols are invalid and, if detected, will set the
receive error bit in the status register.
When transmitting, nibbles from the MII are converted to 5-
bit code groups. The first 16 nibbles obtained from the MII are
the MAC frame preamble. The
ICS1890
replaces the first two
nibbles with the start-of-stream delimiter (the JK symbol
pair). Following the last nibble, the
ICS1890
adds the end-of-
stream delimiter (the TR symbol pair).
When receiving, 5-bit code groups are converted to nibbles
and presented to the MII. If the
ICS1890
detects one or more
invalid symbols, it sets the receive error bit in the status
register. When receiving a frame, the first two 5-bit code
groups received are the start-of-stream delimiter (the JK
symbol pair), the
ICS1890
strips them and substitutes two
nibbles of the normal preamble pattern. The last two 5-bit code
groups are the end-of- stream delimiter (the TR symbol
group), these are stripped from the nibbles presented to the
MAC.
Summary of Contents for PHYceiver ICS1890
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