Micrel, Inc.
KS8721BL/SL
RMII AC Characteristics
Symbol
Parameter
Min
Typ
Max
Units
MHz
%
REF_CLK Frequency
50
REF_CLK Duty Cycle
35
4
65
tSU
tH
TXD[1:0], TX_EN, RXD[1:0], CRS_DV, RXER
ns
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
10/100 BASE-T
Media Dependent Interface
Media Dependent Interface
Transmit Pair
Receive Pair
Receive Pair
Transmit Pair
Modular Connector (RJ45)
Modular Connector (RJ45)
NIC
HUB
(Repeater or Switch)
Figure 1. Straight Through Cable
15
M9999-062509-1.3
June 2009
MICROCHIP [ MICROCHIP ]
