LXT980/980A Dual-Speed, 5-Port Fast Ethernet Repeater
38
Datasheet
2.5.1
PHY Mode Operation
PHY Mode is available at both 10 and 100 Mbps. It allows the LXT980 to interface to a 10 or
100 Mbps MAC. When operating at 100 Mbps, the LXT980 passes the full 56 bits of preamble
through before sending the SFD. When operating at 10 Mbps, the LXT980 sends data across the
MII starting with the 8-bit SFD (no preamble bits).
2.5.2
MAC Mode Operation
MAC Mode (available at 100 Mbps only) allows the user to attach an additional PHY to the
LXT980. In this mode the PHY provides both MII_TXCLK and MII_RXCLK. The MII_TXCLK
must be frequency-locked to the 25 MHz oscillator used by the LXT980. The LXT980 does not
provide an elasticity buffer to compensate for frequency differences. When operating in MAC
mode, the LXT980 generates the full 56 bits of preamble before sending the SFD across the MII.
Table 18. MII (Port 5) Mode & Speed Control
PORT5_SPD
PORT5_SEL
Speed &
Statistics
Mode
High
Low
100 Mbps
MAC
Low
High
10 Mbps
PHY
High
High
100 Mbps
PHY
Figure 8. MII (Port 5) Operation
MII_TXD<3:0>
MII_TXEN
MII_TXER
MII_TXCLK
MII_RXCLK
MII_RXD<3:0>
MII_RXDV
MII_RXER
MII_CRS
MII_COL
MII_TXCLK
MII_RXCLK
MII_RXD<3:0>
MII_RXDV
MII_RXER
MII_CRS
MII_COL
MII_TXD<3:0>
MII_TXEN
MII_TXER
LXT980
10/100
MAC
100 Mbps
PHY
The LXT980 MII port is reversible.
When PHY mode is selected, the
LXT980 acts as the PHY side of the
MII. In this mode an external MAC
sends TX Data to the LXT980 to be
repeated to the network. The
LXT980 repeats network data to the
MAC via the RX Data lines.
When MAC mode is selected, the
LXT980 acts as the MAC side of the
MII. In this mode the LXT980
repeats network data to the PHY via
the TX Data lines.
The external PHY sends data to the
LXT980 to be repeated to the
network via the RX Data lines.
Port 1
Port 2
Port 3
Port 4
Port 5
PHY
TP Ports
MII Port
LXT980
Port 1
Port 2
Port 3
Port 4
Port 5
MAC Mode
TP Ports
MII Port