78Q2123R/F1 Maxim Integrated, 78Q2123R/F1 Datasheet - Page 8

• Manufacturer Part Number: 78Q2123R/F1
• Description: Ethernet ICs
• Manufacturer: Maxim Integrated

Specifications of 78Q2123R/F1

• Rohs: yes

Mbps operation over copper wiring. This function can be enabled via register settings. The
auto-negotiation function defaults to ON and bit MR0.12 (ANEGEN) is high after reset. Software can
disable the auto-negotiation function by writing to bit MR0.12.
The contents of register MR4 are sent to the 78Q2123/78Q2133’s link partner during auto-negotiation via
fast link pulse coding.
The default values of the auto-negotiation registers are set as follows:
idle, or fast link pulses from its link partner. If either idle pattern is detected, the 78Q2123/78Q2133
configure themselves 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 78Q2123/78Q2133 configure
themselves to the highest priority technology common to the two link partners. The technology priorities
Once auto-negotiation is complete, register bits MR18.11:10 will reflect the actual speed and duplex that
was chosen.
If auto-negotiation fails to establish a link for any reason, register bit MR18.12 will reflect this and auto
negotiation will restart from the beginning. Writing a ‘1’ to bit MR0.9 (RANEG) will also cause
auto-negotiation to restart.
78Q2123/78Q2133 Data Sheet
1.4
The 78Q2123/78Q2133 support the auto-negotiation functions of Clause 28 of IEEE-802.3 for 10/100
These default values can be changed by writing different values to the registers, then restarting
auto-negotiation.
With auto-negotiation enabled, the 78Q2123/78Q2133 will start sending fast link pulses at power on, loss
of link or upon a command to restart. At the same time, it will look for either 10BASE-T idle, 100BASE-TX
are, in descending order:
8
Register.Bits
4.8/1.14
4.7/1.13
4.6/1.12
4.5/1.11
0.13
0.12
Auto-Negotiation
0.8
100BASE-TX, Full Duplex
100BASE-TX, Half Duplex
10BASE-T, Full Duplex
10BASE-T, Half Duplex
100 BASE-TX
Speed Select 1 (100 BASE TX)
100BASE-TX
Full Duplex
10 BASE-T
Full Duplex
10 BASE-T
AN Enable
Function
Duplex
Default Value
1 (full duplex)
1 (enabled)
1
1
1
1
DS_21x3_001
Rev. 1.6