2–38
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Transmitter Modules
Refer to
Figure 2–31
for the conversion format. The LSB is transmitted
first.
Figure 2–31
shows the 20-bit encoding.
Figure 2–31. 8B/10B Conversion Format
Reset Condition
The
tx_digitalreset
signal resets the 8B/10B encoder. During reset,
the running disparity registers and the data registers are cleared. Also, the
8B/10B encoder outputs a K28.5 pattern with proper disparity
continuously until
tx_digitalreset
goes low. The
tx_datain
and
tx_ctrlenable
ports are ignored during the reset state. Once out of
reset, the 8B/10B encoder starts the LSByte with a negative disparity
(RD-) bias and the MSByte with a positive disparity (RD+) and transmits
six K28.5 code groups (three on the LSByte and three on the MSByte
encoder) for synchronizing before it starts encoding and transmitting the
data on
tx_datain
.
If the reset signal for the 8B/10B encoder is asserted, the 8B/10B decoder
receiving the data may receive an invalid code error, synchronization
error, control detect, and/or disparity error while
tx_digitalreset
is
high.
Figure 2–32
shows the reset behavior of the 8B/10B encoder. When in
reset (
tx_digitalreset
is high) a K28.5- code group is sent
continuously until
tx_digitalreset
is low. Transmitter channel
pipelining causes some “don’t cares” (10’hxxx) until the first K28.5 is sent
(
Figure 2–32
shows six don’t cares, but the number can vary). Both LSByte
and MSByte transmit three K28.5 code groups each before the data at the
tx_datain
port is encoded and sent out.
8B/10B
Encoder
LSByte
8B/10B
Encoder
MSByte
Dataout[19:1
0]
Dataout[9:
0]
Datain[15:8
]
To Serializer (PISO)
Datain [7:0]
From Byte Serializer
Control signals[0]
Control signals[1]
(1)
(1)