Datasheet

Micrel, Inc. KS8721BL/SL
June 2009
17
M9999-062509-1.3
still sends out its normal transmit pattern from MAC. FEF can be disabled by strapping pin 27 low. Refer to the
“Strapping Options” section.
Media Converter Operation
The KS8721BL/SL is capable of performing media conversion with two parts in a back-to-back RMII loop-back mode as
indicated in the diagram. Both parts are in RMII mode and with RMII BTB asserted (pins 21 and 22 strapped high). One
part is operating in TX mode and the other is operating in FX mode. Both parts can share a common 50MHz oscillator.
Under this operation, auto-negotiation on the TX side prohibits 10BASE-T link-up. Additional options can be
implemented under this operation. Disable the transmitter and set it at tri-state by controlling the high TXD2 pin. In order
to do this, RXD2 and TXD2 pins need to be connected via inverter. When TXD2 pin is high in both the copper and fiber
operation, it is disabled transmit. Meanwhile, the RXD2 pin on the copper side serves as the energy detect and can
indicate if a line signal is detected. TXD3 should be tied low and RXD3 let float. Please contact your Micrel FAE for a
media converter reference design.
Rx
+/-
Tx +/-
FTx
FR
x
Pin
34
TxD
(Fiber Mode)
21 22
Pin
Pin
21 22
50MHz
V
CC
OSC
TxC/
Ref_CLK
TxC/
Ref_CLK
RxD
RxD
V
CC
KS8721BL/SL
KS8721BL/SL
To the SD pin of the
Fiber Module
TxD
Figure 3. Fiber Module