Figure 4-15: Transceiver Datapath in GbE-3.125 Gbps Configuration
FPGA Fabric
tx_coreclk[0]
rx_coreclk[0]
tx_clkout[0]
Transmitter Channel PCS
Transmitter Channel PMA
Receiver Channel PCS
Receiver Channel PMA
Low-Speed Parallel Clock
Parallel Recovered Clock
Low-Speed Parallel Clock
TX Phase
Compensation
FIFO
wrclk rdclk
Byte
SERDES
Byte
SERDES
8B/10B
Encoder
Serializer
Local Clock
Divider
RX Phase
Compensation
FIFO
8B/10B
Decoder
Rate
Match
FIFO
Word
Aligner
Deserializer
CDR
Table 4-4: Transceiver Datapath Clock Frequencies in GbE Configuration
FPGA Fabric-Transceiver Interface
Clock Frequency
Parallel Recovered
Clock and Low-Speed
Parallel Clock
Frequency
High-Speed Serial
Clock Frequency
Data Rate
Functional Mode
125 MHz
125 MHz
625 MHz
1.25 Gbps
GbE-1.25
Gbps
156.25 MHz
312.5 MHz
1562.5 MHz
3.125 Gbps
GbE-3.125
Gbps
8B/10B Encoder
In GbE configuration, the 8B/10B encoder clocks in 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 fed to the serializer.
For more information about the 8B/10B encoder functionality, refer to the
chapter.
Rate Match FIFO
In GbE configuration, the rate match FIFO is capable of compensating for up to ±100 ppm (200 ppm total)
difference between the upstream transmitter and the local receiver reference clock. The GbE protocol requires
that the transmitter send idle ordered sets /I1/ (/K28.5/D5.6/) and /I2/ (/K28.5/D16.2/) during interpacket
gaps, adhering to the rules listed in the IEEE 802.3 specification.
The rate match operation begins after the synchronization state machine in the word aligner indicates that
the synchronization is acquired-by driving the
rx_syncstatus
signal high. The rate matcher always
deletes or inserts both symbols (/K28.5/ and /D16.2/) of the /I2/ ordered sets, even if only one symbol needs
to be deleted to prevent the rate match FIFO from overflowing or underrunning. The rate matcher can insert
or delete as many /I2/ ordered sets as necessary to perform the rate match operation.
Transceiver Protocol Configurations in Cyclone V Devices
Altera Corporation
CV-53004
Gigabit Ethernet Transceiver Datapath
4-14
2013.10.17