Datasheet

 2017 Microchip Technology Inc. DS00002436B-page 33
KSZ8041TL/FTL/MLL
To ensure proper operation, a resistive voltage divider is recommended to adjust the fiber transceiver SD (signal detect)
output voltage swing to match the FXSD pin’s input voltage threshold.
Alternatively, the Far-End Fault feature can be disabled. In this case, the FXSD input pin is tied high to 3.3V to force
100BASE-FX mode.
3.22.2 FAR-END FAULT
A Far-End Fault (FEF) occurs when the signal detection is logically false on the receive side of the fiber transceiver. The
KSZ8041FTL detects a FEF when its FXSD input (pin 48) is between 1V and 1.8V. When a FEF is detected, the
KSZ8041FTL signals its fiber link partner that a FEF has occurred by transmitting a repetitive pattern of 84-ones and 1-
zero. This pattern is used to inform the fiber link partner that there is a faulty link on its transmit side.
By default, FEF is enabled. FEF is disabled by strapping “no FEF” (pin 43) low. See the Strap-In Options section for
detail.
3.23 Back-to-Back Media Converter
A KSZ8041TL/MLL and a KSZ8041FTL can be connected back-to-back to provide a low cost media converter solution.
In back-to-back mode, media conversion is between 100BASE-TX copper and 100BASE-FX fiber. On the copper side,
link up at 10BASE-T is not allowed, and is blocked during auto-negotiation.
3.23.1 MII BACK-TO-BACK MODE
In MII Back-to-Back mode, the KSZ8041TL/MLL interfaces with another KSZ8041TL/MLL, or a KSZ8041FTL to provide
a complete 100 Mbps repeater or media converter solution. The KSZ8041TL/FTL/MLL devices are configured to MII
Back-to-Back mode after they are power-up or reset with the following:
• CONFIG[2:0] (pins 27, 41, 40) set to ‘110’
• A common 25 MHz reference clock connected to XI (pin 15)
• MII signals connected as shown in the following table.
TABLE 3-11: COPPER AND FIBER MODE SELECTION
FXSD Input Voltage Mode
Less than 0.2V Copper mode
Greater than 1V, but less than 1.8V Fiber mode
No signal detected
Far-End Fault generated (if enabled)
Greater than 2.2V Fiber mode
Signal detected
FIGURE 3-10: KSZ8041TL/MLL AND KSZ8041FTL BACK-TO-BACK MEDIA CONVERTER
RX+/-
TX+/-
KSZ8041TL/MLL
(Copper Mode)
RxD
TxD
25MHz
OSC
XI
XI
TxD
RxD
KSZ8041FTL
(Fiber Mode)
FXSD
Fiber
Signal
Detect
Fiber RX
Fiber TX