Intel PCI User Manual

155

Code group and ordered set definitions are defined in clause 36 of the IEEE 802.3z standard. These 

represent special symbols used in the encapsulation of Gigabit Ethernet packets. 

 lists a 

brief description of defined ordered sets for informational purposes only.

The internal Gigabit Media Independent Interface (GMII) is similar to the 10/100 Mb/s Media 

Independent Interface (MII). The GMII uses the MII management interface and registers. These 
common elements of operation allow the Ethernet controller to determine PHY capabilities for any 

supported speed of operation and configuration of the hardware based on those capabilities. 

Most of the MII and GMII signals use the same names, but the width of the RX and TX data busses 

and the semantics of the associated control signals differ between MII and GMII operation. The 
GMII transmit path clocking also differs significantly from MII clocking.

/C/

Configuration

4

General reference to configuration ordered sets, either 
/C1/ or /C2/, which is used during Auto Negotiation to 
advertise & negotiate link operation information between 
link partners. Last two code groups contain config base 
and next page registers.

/C1/

Configuration 1

4

See /C/. Differs from /C2/ in second code group for 
maintaining proper signaling disparity.

/C2/

Configuration 2

4

See /C/. Differs from /C1/ in second code group for 
maintaining proper signaling disparity.

/I/

IDLE

2

General reference to IDLE ordered sets. IDLE characters 
are continually transmitted by the end stations and are 
replaced by encapsulated packet data. The transitions in 
the IDLE stream allow the SerDes to maintain clock and 
symbol synchronization between to link partners.

/I1/

IDLE 1

2

See /I/. Differs from /I2/ in second code group for 
maintaining proper signaling disparity.

/I2/

IDLE 2

2

See /I/. Differs from /I1/ in second code group for 
maintaining proper signaling disparity.

/R/

Carrier_Extend

1

This ordered set is used to indicate carrier extension to 
the receiving PCS. It is also used as part of the 
end_of_packet encapsulation delimiter as well as IPG for 
packets in a burst of packets.

/S/

Start_of_Packet

1

The SPD (start_of_packet delimiter) ordered set is used to 
indicate the starting boundary of a packet transmission. 
This symbol replaces the last byte of the preamble 
received from the MAC layer.

/T/

End_of_Packet

1

The EPD (end_of_packet delimiter) is comprised of three 
ordered sets. The /T/ symbol is always the first of these 
and indicates the ending boundary of a packet.

/V/

Error_Propagation

1

The /V/ ordered set is used by the PCS to indicate error 
propagation between stations. This is normally intended to 
be used by repeaters to indicate collisions.