KSZ8091RNA / KSZ8091RND 10Base-T/100Base-TX Evaluation Board User’s Guide
Micrel, Inc.
August 17, 2012
Rev.
1.0
7/11
4.1 RMII (Reduced Media Independent Interface)
The KSZ8091RNA-EVAL / KSZ8091RND-EVAL accesses RMII data from the MII connector J4.
This connector is also optionally used for MDC/MDIO management bus access and for 5V power
to the evaluation board. Figure 2 shows the KSZ8091RNA-EVAL / KSZ8091RND-EVAL
connected to the Micrel KSZ8463RLI Evaluation Board through connector J4.
Figure 2. KSZ8091RNA-EVAL interfacing with KSZ8463RLI Evaluation Board
Two RMII clocking modes are available with the KSZ8091RNA and KSZ8091RND. The
KSZ8091RNA powers up in RMII-25MHz Mode, while the KSZ8091RND powers up in RMII-
50MHz mode. After power-up, both KSZ8091RNA and KSZ8091RND can be programmed via
PHY register 1Fh bit [7] to either 25MHz mode or 50MHz mode.
In 25MHz Mode, a 25MHz crystal is connected to the XI and XO pins of the KSZ8091.
(Alternatively, a 25 MHz oscillator may drive XI.) The KSZ8091 outputs a 50 MHz RMII Reference
Clock on its REF_CLK pin. REF_CLK drives pin 9 of the MII connector J4, for connection to a
MAC RMII device on an attached board.
In 50MHz Mode, the KSZ8091 receives the 50MHz RMII Reference Clock as an input on the XI
pin from pin 12 of the MII connector J4. This clock is sourced from a MAC device (or a separate
clock source) on an attached board. No local 25MHz crystal or oscillator is used.
These two modes have different component installation requirements on the evaluation board, as
shown in Table 1.
