Datasheet

Micrel, Inc. KS8721BL/SL
June 2009
15
M9999-062509-1.3
RMII AC Characteristics
Symbol Parameter Min Typ Max Units
REF_CLK Frequency 50 MHz
REF_CLK Duty Cycle 35 65 %
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_CLK
Rising Edge
2 ns
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.
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
feature is controlled by register 1f:13. See “Register 1fh–100BASE-TX PHY Controller” section for details.
10/100 BASE-T
Media Dependent Interface
10/10
0
BASE-T
Media Dependent Interface
Transmit Pair
Receive Pair
Transmit Pair
Receive Pair
Modular Connector (RJ45)
NIC
Modular Connector (RJ45)
HUB
(Repeater or Switch)
Figure 1. Straight Through Cable