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tx_datak
is low, the 8B/10B encoder block encodes the byte at the
tx_parallel_data
signal as data
(Dx.y). When tx_datak is high, the 8B/10B encoder encodes the input data as a Kx.y code group. The rest
of the
tx_parallel_data
bytes are encoded as a data word (Dx.y).
Figure 1-26: Control Word and Data Word Transmission
The second 0xBC is encoded as a control word (K28.5).
tx_datak
clock
tx_datain[7:0]
code group
83
78
BC
BC
0F
00
BF
3C
D3.4
D24.3
D28.5
K28.5
D15.0
D0.0
D31.5
D28.1
The IEEE802.3 8B/10B encoder specification identifies only a set of 8-bit characters for which you
must assert
tx_datak
. If you assert
tx_datak
for any other set of bytes, the 8B/10B encoder
Note:
might encode the output 10-bit code as an invalid code (it does not map to a valid Dx.y or Kx.y code),
or unintended valid Dx.y code, depending on the value entered. It is possible for a downstream
8B/10B decoder to decode an invalid control word into a valid Dx.y code without asserting code
error flags.
Reset Condition
The
reset_tx_digital
signal resets the 8B/10B encoder. During reset, the running disparity and data
registers are cleared. Also, the 8B/10B encoder outputs a K28.5 pattern from the RD– column continuously
until
reset_tx_digital
is deasserted. The input data and control code from the FPGA fabric is ignored
during the reset state. After reset, the 8B/10B encoder starts with a negative disparity (RD–) and transmits
three K28.5 code groups for synchronization before it starts encoding and transmitting the data on its output.
While
reset_tx_digital
is asserted, the downstream 8B/10B decoder that receives the data
might observe synchronization or disparity errors.
Note:
Encoder Output During Reset Sequence
When in reset (
reset_tx_digital
is high), a K28.5- (K28.5 10-bit code group from the RD– column)
is sent continuously until
reset_tx_digital
is low. Because of some pipelining of the transmitter
channel PCS, some “don’t cares” (10’hxxx) are sent before the three synchronizing K28.5 code groups. User
data follows the third K28.5 code group.
Transceiver Architecture in Cyclone V Devices
Altera Corporation
CV-53001
Reset Condition
1-32
2013.05.06