LXT971A 3.3V Dual-Speed Fast Ethernet Transceiver
3.6.2
Transmit Enable
The MAC must assert TX_EN the same time as the first nibble of preamble, and de-assert TX_EN
after the last bit of the packet.
3.6.3
Receive Data Valid
The LXT971A asserts RX_DV when it receives a valid packet. Timing changes depend on line
operating speed:
•
For 100BASE-TX links, RX_DV is asserted from the first nibble of preamble to the last nibble
of the data packet.
•
For 10BT links, the entire preamble is truncated. RX_DV is asserted with the first nibble of the
Start of Frame Delimiter (SFD) “5D” and remains asserted until the end of the packet.
3.6.4
Carrier Sense
Carrier Sense (CRS) is an asynchronous output. It is always generated when a packet is received
from the line and in half-duplex mode when a packet is transmitted.
summarizes the
conditions for assertion of carrier sense, collision, and data loopback signals.
Carrier sense is not generated when a packet is transmitted and in full-duplex mode.
3.6.5
Error Signals
When LXT971A is in 100 Mbps mode and receives an invalid symbol from the network, it asserts
RX_ER and drives “1110” on the RXD pins.
When the MAC asserts TX_ER, the LXT971A drives “H” symbols out on the TPFOP/N pins.
3.6.6
Collision
The LXT971A asserts its collision signal, asynchronously to any clock, whenever the line state is
half-duplex and the transmitter and receiver are active at the same time.
summarizes the
conditions for assertion of carrier sense, collision, and data loopback signals.
Datasheet
Document #: 249414
Revision #: 002
Rev. Date: August 7, 2002
33
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