40 pin D-Subminiature Connector using Jack-screws

Ethernet MII Pin Out

Ethernet Bus MII Pin-Out

The Media Independent Interface [MII] is a 40 pin Miniature-D connector. The pinout for the 40 pin D is shown below.
Pins 2 and pin 3 of the MII interface form the MDIO interface.
The MII is used to transition between a MAC [Media Access Control] and Ethernet physical devices [PHY].

Ethernet MII Pin Out
Pin Number name Signal Description
1 Power +5 Vdc/ 3.3 Vdc
2 MDIO MII Data Input/Output
3 MDC MII Data Clock
4 RxD 3 Receive Data 3
5 RxD 2 Receive Data 2
6 RxD 1 Receive Data 1
7 RxD 0 Receive Data 0
8 Rx_DV Rx Data Valid
9 Rx_CLK Rx Clock
10 Rx_ER Rx Error
11 Tx_ER Tx Error
12 Tx_CLK Tx Clock
13 Tx_EN Tx Enable
14 TxD 0 Transmit Data 0
15 TxD 1 Transmit Data 1
16 TxD 2 Transmit Data 2
17 TxD 3 Transmit Data 3
18 COL Collision
19 CRS Carrier Sense
20 Power +5 Vdc/ +3.3 Vdc
21 Power +5 Vdc/ +3.3 Vdc
22 GND Signal Ground
35 GND Ground
38 GND Signal Ground
40 Power +5 Vdc/ +3.3 Vdc

Although the MII interface uses a 40 position D-subminiature connector, it is not a standard D-type connector.
The standard D-type connector is not available in 40-position contacts, and this connector differs in other ways.
The most common number of positions for a D-type connector is 9, 15, 25 and 37 contacts;
Refer to Dsub Connector positions for more details on connector shape and dimensions.
There are also other differences in the physical shape of the connector, but manufacturers may still list them under D type connectors.
The D-shell of the connector is not as rounded as a standard D-type connector, although it still appears to be a D-sub shape.
The pin receptacles of this connector style are square, while the true D-sub receptacles are round.

Dsub Connector manufacturers for companies making D-Sub Connectors.
All other Connector types; Connector manufacturers.

Back to the 10/100 Base Ethernet page, or
1000 base Ethernet page for additional pinout tables and interface descriptions.

Note this connector is also used with some SCSI interconnects, of course the pinout differs.
Latch bars or jackscrews are available on many connectors of this style [the graphic uses latch-bars].

40 Position D-Subminiature Connector, Mechanical figure Amp Connector
Physical Interface Connector

The dimensions for the connector as pointed out in the attached graphic are as follows;
E: 1.580, F: 0.950, and overall length dimension G: 1.815 inches.

The MII connector is normally only found on OEM gear, or servers.
The connector is some what large, so you wouldn't expect to find it on a small NICK card.
Check the IEEE802.3 specification for additional details on the Mechanical Ethernet standard.

PC motherboard

Distributor rolodex Electronic Components Electronic Equipment EDA CDROM Software Engineering Standards, BOB card Cabled Computer Bus Electronic Engineering Design Table Conversion DB9-to-DB25.
DistributorsComponents Equipment Software Standards Buses Design Reference

Modified 6/13/15
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