KSZ8081RNA Datasheet, PDF (16/52 Pages) Microchip Technology – 10BASE-T/100BASE-TX PHY with RMII Support

KSZ8081RNA/RND
3.3 Back-to-Back Mode – 100 Mbps Copper Repeater
Two KSZ8081RNA/RND devices can be connected back-to-back to form a managed 100BASE-TX copper repeater.
FIGURE 3-4:
KSZ8081RNA/RND AND KSZ8081RNA/RND RMII BACK-TO-BACK COPPER
REPEATER
RXP/RXM
RxD
TXP/TXM
KSZ8081RNA/RND
(COPPER MODE)
TxD
XI
XI
TXP/TXM
KSZ8081RNA/RND
(COPPER MODE)
TxD
RXP/RXM
RxD
50MHz
OSC
3.3.1 RMII BACK-TO-BACK MODE
In RMII back-to-back mode, a KSZ8081RNA/RND interfaces with another KSZ8081RNA/RND to provide a 100 Mbps
copper repeater solution.
The KSZ8081RNA/RND devices are configured to RMII back-to-back mode after power-up or reset, and software pro-
gramming, with the following:
• A common 50 MHz reference clock connected to XI (Pin 8)
• Register 1Fh, Bit [7] programmed to ‘1’ to select RMII – 50 MHz clock mode for KSZ8081RNA
KSZ8081RND is set to RMII – 50 MHz clock mode as the default after power up or hardware reset.
• Register 16h, Bits [6] and [1] programmed to ‘1’ and ‘1’, respectively, to enable RMII back-to-back mode.
• RMII signals connected as shown in Table 3-2.
TABLE 3-2: RMII SIGNAL CONNECTION FOR RMII BACK-TO-BACK MODE (100BASE-TX
COPPER REPEATER)
KSZ8081RNA/RND (100BASE-TX Copper)
[Device 1]
KSZ8081RNA/RND (100BASE-TX Copper)
[Device 2]
Pin Name
CRS_DV
RXD1
RXD0
TXEN
TXD1
TXD0
Pin Number
15
12
13
19
21
20
Pin Type
Output
Output
Output
Input
Input
Input
Pin Name
TXEN
TXD1
TXD0
CRS_DV
RXD1
RXD0
Pin Number
19
21
20
15
12
13
Pin Type
Input
Input
Input
Output
Output
Output
DS00002199A-page 16
 2016 Microchip Technology Inc.