ADM7008
Function Description
at least two idle code-groups are detected. Once at least two idle code groups are
detected, RXER and CRS become deasserted.
Far-End Fault
Auto negotiation provides a mechanism for transferring information from the Local
Station to the link Partner that a remote fault has occurred for 100Base-TX. As auto
negotiation is not currently specified for operation over fiber, the far end fault indication
function (FEFI) provides this capability for 100Base-FX applications.
A remote fault is an error in the link that one station can detect while the other cannot.
An example of this is a disconnected wire at a station’s transmitter. This station will be
receiving valid data and detect that the link is good via the link integrity monitor, but will
not be able to detect that its transmission is not propagating to the other station.
A 100Base-FX station that detects such a remote fault may modify its transmitted idle
stream from all ones to a group of 84 ones followed by a single 0. This is referred to as
the FEFI idle pattern.
The FEFI function is controlled by bit 3 of register 11h. It is initialized to 1 (encoded) if
the SELFX pin is at logic high level during power on reset. If the FEFI function is
enabled the ADM7008 will halt all current operations and transmit the FEFI idle pattern
when FOSD signal is de-asserted following a good link indication from the link integrity
monitor. FOSD signal is generated internally from the internal signal detect circuit.
Transmission of the FEFI idle pattern will continue until link up signal is asserted. If
three or more FEFI idle patterns are detected by the ADM7008, then bit 4 of the Basic
mode status register (address 1h) is set to one until read by management. Additionally,
upon detection of far end fault, all receive and transmit MII activity is disabled/ignored.
3.1.3 100Base-TX Transmitter
ADM7008 implements a TP-PMD compliant transceiver for 100Base-TX operation. The
differential transmit driver is shared by the 10Base-T and 100Base-TX subsystems. This
arrangement results in one device that uses the same external magnetics for both the
10Base-T and the 100Base-TX transmission with simple RC component connections.
The individually wave-shaped 10Base-T and 100Base-TX transmit signals are
multiplexed in the transmission output driver selection.
ADM7008 100Base-TX transmission driver implements MLT-3 translation and wave-
shaping functions. The rise/fall time of the output signal is closely controlled to conform
to the target range specified in the ANSI TP-PMD standard.
3.1.4 100Base-FX Receiver
Signal is received through PECL receiver inputs from fiber transceiver, and directly
passed to clock recovery circuit for data/clock recovery. Scrambler/de-scrambler is
bypassed in 100Base-FX.
ADMtek Inc.
3-7
ETC [ ETC ]
