ADM7008
Function Description
Valid Data Signal
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 deasserted.
Receive Errors
The RXER signal is used to communicate receiver error conditions. While the receiver is
in a state of holding RXDV asserted, the RXER will be asserted for each code word that
does not map to a valid code-group.
100Base-X Link Monitor
The 100Base-X link monitor function allows the receiver to ensure that reliable data is
being received. Without reliable data reception, the link monitor will halt both transmit
and receive operations until such time that a valid link is detected.
The ADM7008 performs the link integrity test as outlined in IEEE 100Base-X (Clause 24)
link monitor state diagram. The link status is multiplexed with 10 Mbits/s link status to
form the reportable link status bit in serial management register 1h, and driven to the
LNKACT pin.
When persistent signal energy is detected on the network, the logic moves into a Link-
Ready state after approximately 500 us, and waits for an enable from the auto negotiation
module. When receive, the link-up state is entered, and the transmission and reception
logic blocks become active. Should auto negotiation be disabled, the link integrity logic
moves immediately to the link-up state after entering the link-ready state.
Carrier Sense
Carrier sense (CRS) for 100 Mbits/s operation is asserted upon the detection of two
noncontiguous zeros occurring within any 10-bit boundary of the received data stream.
The carrier sense function is independent of symbol alignment. In switch mode, CRS is
asserted during either packet transmission or reception. For repeater mode, CRS is
asserted only during packet reception. When the idle symbol pair is detected in the
received data stream, CRS is deasserted. In repeater mode, CRS is only asserted due to
receive activity. CRS is intended to encapsulate RXDV.
Bad SSD Detection
A bad start of stream delimiter (Bad SSD) is an error condition that occurs in the
100Base-X receiver if carrier is detected (CRS asserted) and a valid /J/K set of code-
group (SSD) is not received.
If this condition is detected, then the ADM7008 will assert RXER and present RXD[3:0]
= 1110 to the internal MII for the cycles hat correspond to received 5B code-groups until
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