Ethernet PHY
931
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Ethernet Controller
highest performance protocol based on the advertised ability of the Link Partner. If a different auto-
negotiation configuration is required other than the reset initialization values, the application can customize
the configuration of the ANEN bit and ANMODE bit field as described in
. The values of
ANEN and ANMODE determine whether the PHY is forced into a specific mode, or if Auto-negotiation
advertises a specific ability (or abilities) as listed in
and
Table 15-20. Forced Mode Configurations
ANEN Value
ANMODE
Forced Mode
0
0x0
10Base-T, Half-Duplex
0
0x1
10Base-T, Full-Duplex
0
0x2
100Base-TX, Half-Duplex
0
0x3
100Base-TX, Full-Duplex
Table 15-21. Advertised Mode Configurations
ANEN Value
ANMODE
Advertised Mode
1
0x0
10Base-T, Half/Full-Duplex
1
0x1
100Base-TX, Half/Full-Duplex
1
0x2
10Base-T, Half Duplex 100Base-TX, Half Duplex
1
0x3
10Base-T, Half/Full-Duplex 100Base-TX, Half/Full-Duplex
15.4.2.2 Auto-MDIX
The PHY automatically determines whether or not it needs to cross over between pairs so that an external
crossover cable is not required. If the PHY communicates with a device that implements MDI/MDIX
crossover, a random algorithm as described in IEEE 802.3 determines which device performs the
crossover. Auto-MDIX is enabled by default at reset. If a different auto-MDIX configuration is required
other than the reset initialization, the application can customize the configuration as described in
. Neither Auto-Negotiation nor Auto-MDIX is required to be enabled in forcing crossover of
the MDI pairs. Auto-MDIX can be used in the forced 100Base-TX mode. Because in modern networks all
the nodes are 100Base-TX, having the Auto-MDIX working in the forced 100Base-TX mode resolves the
link faster without the need for the long Auto-Negotiation period.
15.4.2.3 Isolate Mode
The PHY can be put into Isolate mode by writing ISOLATE bit of the Ethernet PHY Basic Mode Control -
MR0 (EPHYBMCR) register, address 0x000. When in the Isolate mode, the PHY does not respond to
packet data present at the internal interface to the Ethernet MAC. When in isolate mode, the PHY
continues to respond to all management transactions and the PMD output pair does not transmit packet
data, but continues to source 100Base-TX scrambled idles or 10Base-T normal link pulses. The PHY can
auto-negotiate or parallel detect on the receive signal at the PMD input pair. A valid link can be
established for the receiver even when the PHY is in Isolate mode.
15.4.2.4 LED Interface
The PHY supports three configurable light emitting diode (LED) pins to indicate link status of a port. The
Ethernet PHY LED Configuration - MR37 (EPHYLEDCFG) register, address 0x025 can be used to assign
different functions to each LED. Each LED can be configured to be active during one of these events:
•
Link OK (0x0)
•
RX/TX Activity (0x1)
•
TX Activity (0x2)
•
RX Activity (0x3)
•
Collision (0x4)
•
100-BASE TX speed (0x5)