Autonegotiation And Parallel Detection; Automatic Crossover And Polarity Detection; Table 2.1 Supported Mdi Pair Combinations - Renesas R-IN32M4-CL2 User Manual

R-IN32M4-CL2 User's Manual Gigabit Ethernet PHY Edition
2.1.2

Autonegotiation and Parallel Detection

The GbE-PHY supports twisted pair autonegotiation, as defined by IEEE 802.3-2008 Clause 28. The autonegotiation
process evaluates the advertised capabilities of the local PHY and its link partner to determine the best possible operating
mode. In particular, autonegotiation can determine speed, duplex configuration, and master or slave operating modes for
1000BASE-T.
If the link partner does not support autonegotiation, the GbE-PHY automatically uses parallel detection to select the
appropriate link speed.
Autonegotiation is disabled by clearing register 0, bit 12. When autonegotiation is disabled, the state of register bits 0.6,
0.13, and 0.8 determine the device operating speed and duplex mode.
Caution: While 10BASE-T and 100BASE-TX do not require autonegotiation, IEEE 802.3-2008 Clause 40
has defined 1000BASE-T to require autonegotiation.
2.1.3

Automatic Crossover and Polarity Detection

For trouble-free configuration and management of Ethernet links, the GbE-PHY includes a robust automatic crossover
detection feature for all three speeds on the twisted pair interface (10BASE-T, 100BASE-TX, and 1000BASE T). Known
as HP Auto-MDIX, the function is fully compliant with Clause 40 of IEEE 802.3-2008.
Additionally, the device detects and corrects polarity errors on all MDI pairs — a useful capability that exceeds the
requirements of the standard.
Both HP Auto-MDIX detection and polarity correction are enabled in the device by default. Default settings can be
changed using device register bits 18.5:4. Status bits for each of these functions are located in register 28.
Caution: The GbE-PHY can be configured to perform HP Auto-MDIX, even when autonegotiation is
disabled and the link is forced into 10/100 speeds. To enable this feature, set register 18.7 to
0. To use the feature, also set register 0.12 to 0.
The HP Auto-MDIX algorithm successfully detects, corrects, and operates with any of the MDI
wiring pair combinations listed in the following table, which shows that twisted pair A (of four
twisted pairs A, B, C, and D) is connected to the RJ45 connector 1,2 in normal MDI mode.

Table 2.1 Supported MDI Pair Combinations

1, 2 3, 6
A B
B A
A B
B A
R18UZ0043EJ0100
Mar 4, 2016
RJ45 Connections
4, 5 7, 8
C D
D C
D C
C D
Normal MDI
Normal MDI-X
Normal MDI with pair swap on C and D pair
Normal MDI-X with pair swap on C and D pair
2. Functional Descriptions
Mode
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