Draft 6/5/00
Block Diagram Description
2-13
Copyright 2000 by LSI Logic Corporation. All rights reserved.
There is no FBI operation in the 10 Mbits/s mode.
2.2.2.3 Selection of MII or FBI
FBI Selection –
The FBI is automatically enabled when the 4B5B
encoder/decoder is bypassed. Bypassing the encoder/decoder passes
the 5B symbols between the receiver/transmitter directly to the FBI
without any alterations or substitutions. To bypass the 4B5B
encoder/decoder, set the Bypass Encoder bit (BYP_ENC) in the MI serial
port Configuration 1 register.
When the FBI is enabled, it may also be desirable to bypass the
scrambler/descrambler and disable the internal CRS loopback function.
To bypass the scrambler/descrambler, set the Bypass Scrambler bit
(BYP_SCR) in the MI serial port Configuration 1 register. To disable the
internal CRS loopback, set the TX_EN to CRS loopback disable bit
(TXEN_CRS) in the MI serial port Configuration 1 register.
MII Selection –
To disable the MII (and FBI) inputs and outputs, set the
MII_DIS bit in the MI serial port Control register. When the MII is
disabled, the MII and FBI inputs are ignored, and the MII, FBI, and TPI
outputs are placed in a high-impedance state. The MII pins affected are:
RX_CLK
RXD[3:0]
RX_DV
RX_ER
COL
If the MI address lines, MDA[4:0]n, are pulled HIGH during reset or
powerup, the L80223 powers up and resets with the MII and FBI
disabled. Otherwise, the L80223 powers up and resets with the MII and
FBI enabled.
In addition, when the R/J_CFG bit in the MI serial port Configuration 1
register is LOW, the RX_EN/JAMn pin is configured for RX_EN
operation. If the RX_EN pin is LOW in this situation, the MII controller
interface outputs are placed in the high-impedance state.