Datasheet
KSZ8041TL/FTL/MLL
DS00002436B-page 34 2017 Microchip Technology Inc.
3.23.2 RMII BACK-TO-BACK MODE (KSZ8041TL/FTL ONLY)
In RMII Back-to-Back mode, the KSZ8041TL interfaces with another KSZ8041TL, or a KSZ8041FTL to provide a com-
plete 100 Mbps repeater or media converter solution. The KSZ8041TL/FTL devices are configured to RMII Back-to-
Back mode after they are power-up or reset with the following:
• CONFIG[2:0] (pins 27, 41, 40) set to ‘101’
• A common 50 MHz reference clock connected to REFCLK (pin 15)
• RMII signals connected as shown in the following table.
RMII Back-to-Back mode provides an option to disable the fiber side when the copper side is down. This, effectively,
produces a link fault propagation for media converter applications, such that a copper side link down will automatically
disable the fiber side. This KSZ8041TL/FTL feature functions as follows:
• On the KSZ8041TL copper side, RXD2 (pin 21) indicates if there is energy detected at the receive inputs of the
copper port. RXD2 outputs a low if there is no energy detected (cable disconnected), and outputs a high if there is
energy detected (cable connected).
• The RXD2 output of the KSZ8041TL copper side drives the input of an inverter, and the output of the inverter
drives the TXD2 (pin 38) input of the KSZ8041FTL fiber side. The fiber side transmitter is disabled if the TXD2
input is high.
The TXD3 and TXD2 pins should be pulled down with 1K resistors, and RXD3 and RXD2 pins should be left floating, if
they are not used.
TABLE 3-12: MII SIGNAL CONNECTION FOR MII BACK-TO-BACK MODE
KSZ8041MLL (100BASE-TX copper)
KSZ8041TL (100BASE-TX copper)
KSZ8041MLL (100BASE-TX copper)
KSZ8041TL (100BASE-TX copper)
KSZ8041FTL (100BASE-FX fiber)
Pin Name Pin Number Pin Type Pin Name Pin Number Pin Type
RXC 28 Output TXC 33 Input
RXDV 27 Output TXEN 34 Input
RXD3 20 Output TXD3 39 Input
RXD2 21 Output TXD2 38 Input
RXD1 22 Output TXD1 36 Input
RXD0 23 Output TXD0 35 Input
TXC 33 Input RXC 28 Output
TXEN 34 Input RXDV 27 Output
TXD3 39 Input RXD3 20 Output
TXD2 38 Input RXD2 21 Output
TXD1 36 Input RXD1 22 Output
TXD0 35 Input RXD0 23 Output
TABLE 3-13: RMII SIGNAL CONNECTION FOR RMII BACK-TO-BACK MODE
KSZ8041TL (100BASE-TX copper)
KSZ8041TL (100BASE-TX copper)
KSZ8041FTL (100BASE-FX fiber)
Pin Name Pin Number Pin Type Pin Name Pin Number Pin Type
CRSDV 27 Output TXEN 34 Input
RXD1 22 Output TXD1 36 Input
RXD0 23 Output TXD0 35 Input
TXEN 34 Input CRSDV 27 Output
TXD1 36 Input RXD1 22 Output
TXD0 35 Input RXD0 23 Output