Maxim Integrated 78Q8430 Software Driver - Manual (Page 40)

78Q8430 Software Driver Development Guidelines UG_8430_004
Table 7: Auto-negotiation Registers Default Values
Register Field / Function Default Value
Speed Selection 1 (100Base-TX)
Auto-negotiation Enable 1 (enabled)
MR0
Duplex Mode 1 (full duplex)
100BASE-TX Full Duplex 1
100BASE-TX Half Duplex 1
10BASE-T Full Duplex 1
MR4 / MR1
10BASE-T 1
When auto-negotiation is enabled, the 78Q8430 sends the contents of the Auto-negotiation
Advertisement Register, MR4, to it’s link partner using fast link pulse coding at power on, loss of link or on
a command to restart auto-negotiation. At the same time, it looks for either 10BASE-T idle, 100BASE-TX
idle, or fast link pulses from its link partner. If either idle pattern is detected, the 78Q8430 configures itself
in half-duplex mode at the appropriate speed. If it detects fast link pulses, it decodes and analyzes the
link code transmitted by the link partner. When three identical link code words are received (ignoring the
acknowledge bit) the link code word is stored in register MR5. Upon receiving three more identical link
code words, with the acknowledge bit set, the 78Q8430 configures itself to the highest priority technology
common to the two link partners. The technology priorities are, in descending order:
100BASE-TX, Full Duplex
100BASE-TX, Half Duplex
10BASE-T, Full Duplex
10BASE-T, Half Duplex
When auto-negotiation is complete, the MR18 Rate Indication and Duplex Indication bits reflect the actual
negotiated speed and duplex mode.
If auto-negotiation fails to establish a link for any reason, the MR18 Auto-negotiation Fail Indication bit
reflects this and auto negotiation restarts from the beginning.
7.4.1 Disable Auto-negotiation
Use the following procedure to disable the auto-negotiation function:
STEP 1: Use procedure 7.2 to read the value of the MR0 register.
STEP 2: Clear the MR0 Auto-negotiation Enable bit to disable auto-negotiation.
STEP 3: Use procedure
7.1 to write the modified value back to the MR0 register.
7.4.2 Enable Auto-negotiation
The auto-negotiation function defaults to enabled after reset. Use the following procedure to re-enable
the function if it has been disabled:
STEP 1: Use procedure 7.2 to read the value of the MR0 register.
STEP 2: Set the MR0 Auto-negotiation Enable bit to enable auto-negotiation.
STEP 3: Use procedure
7.1 to write the modified value back to the MR0 register.
7.4.3 Restart Auto-negotiation
Normally, the auto-negotiation process is started at power up or loss of link. Use the following process to
restart the process at other times:
40 Rev. 1.0