User guide

8B/10B Encoding for GbE, GbE with IEEE 1588v2
The 8B/10B encoder clocks 8-bit data and 1-bit control identifiers from the transmitter phase
compensation FIFO and generates 10-bit encoded data. The 10-bit encoded data is sent to the PMA.
The IEEE 802.3 specification requires GbE to transmit idle ordered sets (/I/) continuously and repetitively
whenever the gigabit media-independent interface (GMII) is idle. This transmission ensures that the
receiver maintains bit and word synchronization whenever there is no active data to be transmitted.
For the GbE protocol, the transmitter replaces any /Dx.y/ following a /K28.5/ comma with either a /D5.6/
(/I1/ ordered set) or a /D16.2/ (/I2/ ordered set), depending on the current running disparity. The
exception is when the data following the /K28.5/ is /D21.5/ (/C1/ ordered set) or /D2.2/ (/C2/) ordered set.
If the running disparity before the /K28.5/ is positive, an /I1/ ordered set is generated. If the running
disparity is negative, a /I2/ ordered set is generated. The disparity at the end of a /I1/ is the opposite of that
at the beginning of the /I1/. The disparity at the end of a /I2/ is the same as the beginning running
disparity immediately preceding transmission of the idle code. This sequence ensures a negative running
disparity at the end of an idle ordered set. A /Kx.y/ following a /K28.5/ does not get replaced.
Note: /D14.3/, /D24.0/, and /D15.8/ are replaced by /D5.6/ or /D16.2/ (for I1 and I2 ordered sets). D21.5
(/C1/) is not replaced.
Figure 2-28: Idle Ordered-Set Generation Example
K28.5 D14.3 K28.5 D24.0 K28.5 D15.8 K28.5 D21.5
tx_datain [ ]
clock
Dx.y
Dx.y K28.5 D5.6 K28.5 D16.2 K28.5 D16.2 K28.5
tx_dataout
Ordered Set
D21.5
/I1/ /I2/ /I2/ /C 2/
Related Information
8B/10B Encoder on page 5-40
Reset Condition for 8B/10B Encoder in GbE, GbE with IEEE 1588v2
After deassertion of tx_digitalreset, the transmitters automatically transmit at least three /K28.5/
comma code groups before transmitting user data on the tx_parallel_data port. This transmission
could affect the synchronization state machine behavior at the receiver.
Depending on when you start transmitting the synchronization sequence, there could be an even or odd
number of /Dx.y/ code groups transmitted between the last of the three automatically sent /K28.5/ code
groups and the first /K28.5/ code group of the synchronization sequence. If there is an even number
of /Dx.y/code groups received between these two /K28.5/ code groups, the first /K28.5/ code group of the
synchronization sequence begins at an odd code group boundary. The synchronization state machine
treats this as an error condition and goes into the loss of synchronization state.
2-100
8B/10B Encoding for GbE, GbE with IEEE 1588v2
UG-01143
2015.05.11
Altera Corporation
Implementing Protocols in Arria 10 Transceivers
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