Datasheet

 2018 Microchip Technology Inc. DS00002813A-page 15
KSZ8721BL/SL
FIGURE 3-2: CROSSOVER CABLE
3.20 Power Management
The KSZ8721BL/SL offers the following modes for power management:
• Power-Down Mode: This mode can be achieved by writing to Register 0.11 or pulling pin 30 PD# low.
• Power-Saving Mode: This mode can be disabled by writing to Register 1fh.10. The KSZ8721BL/SL turns off
everything except for the Energy Detect and PLL circuits when the cable is not installed. In other words, the
KSZ8721BL/SL shuts down most of the internal circuits to save power if there is no link. Power-saving mode is in
the most effective state when auto-negotiation mode is enabled.
3.21 100BT FX Mode
Please contact your local field application engineer (FAE) for a reference schematic on fiber connection.
100BT FX mode is activated when FXSD/FXEN is higher than 0.6V (this pin has a default pull down). Under this mode,
the auto-negotiation and auto-MDI-X features are disabled.
In fiber operation, the FXSD pin should connect to the signal detect (SD) output of the fiber module. The internal thresh-
old of FXSD is around 1/2 VDD ±50 mV (1.25V ±0.05V). Above this level, the fiber signal is considered detected.
The operation is summarized in Table 3-3:
Receive Pair Receive Pair
Transmit Pair
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Transmit Pair
10/100 Ethernet
Media Dependent Interface
10/100 Ethernet
Media Dependent Interface
Modular Connector (RJ-45)
HUB
(Repeater or Switch)
Modular Connector (RJ-45)
HUB
(Repeater or Switch)
Crossover
Cable