Datasheet

KSZ8721BL/SL
DS00002813A-page 14  2018 Microchip Technology Inc.
3.18 Unused RMII Pins
Input Pins TXD[2:3] and TXER are pull-down to GND
Output Pins RXD[2:3] and RXC are no connect.
Note that the RMII pin needs to be pulled up to enable RMII mode.
3.19 Auto-Crossover (Auto-MDI/MDI-X)
Automatic MDI/MDI-X configuration is intended to eliminate the need for crossover cables between similar devices. The
assignment of pinouts for a 10/100 BASE-T crossover function cable is shown below.
This feature eliminates the confusion in applications by allowing the use of both straight and crossover cables. This fea-
ture is controlled by register 1f:13. See Table 4-13 for details.
FIGURE 3-1: STRAIGHT THROUGH CABLE
t
SU
TXD[1:0], TX_EN, RXD[1:0], CRS_DV, RXER 4 — — ns
t
H
TXD[1:0], TX_EN, RXD[1:0], CRS_DV, RXER
Data Hold from REF_CLKRising Edge
2——ns
TABLE 3-2: RMII AC CHARACTERISTICS
Symbol Parameter Min. Typ. Max. Units
Receive PairTransmit Pair
Receive Pair
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Transmit Pair
Modular Connector
(RJ-45)
NIC
Straight
Cable
10/100 Ethernet
Media Dependent Interface
10/100 Ethernet
Media Dependent Interface
Modular Connector
(RJ-45)
HUB
(Repeater or Switch)