Altera Stratix GX Transceiver - Manual (Page 167)

Altera Corporation 6–13
January 2005 Stratix GX Transceiver User Guide
GigE Mode
At time n + 4, because the current disparity is negative, a K28.5 from the
RD-
column is expected, but a K28.5 code from the RD+ is received
instead. This disparity prompts the rx_disperr signal to go high
during time n + 4 to indicate that this particular K28.5 code contained a
disparity error. The current running disparity at the end of time n + 4 is
negative because a K28.5 code from the RD+ column was received. Based
on the current running disparity at the end of time n + 5, a positive
disparity K28.5 code (from the RD-) column is expected at time n + 5.
Figure 6–13. Disparity Error
Control Detect
The 8B/10B decoder differentiates between data and control codes using
the rx_ctrldetect port. Although this port is optional, there is no way
of differentiating a Dx.y code group from a Kx.y code group if the port
is unused.
Figure 6–14 shows an example waveform demonstrating the receipt of a
K28.5 code (BC + ctrl). The rx_ctrldetect=1’b1 port is aligned with
8’hbc , indicating that it is a control code. The rest of the code received is
data.
clock
rx_out[7:0 ]
rx_disperr
BC BC BC BC BC BC
rx_ctrldetect
BC
Expected RD code
rx_in 17C 283 17C 283 283 283 17C 17C
RD- RD+ RD+ RD- RD- RD- RD+ RD-
RD code received RD- RD+ RD+ RD- RD+ RD- RD+ RD-
n n+1 n+2 n+3 n+4 n+5 n+6 n+7
rx_errdetect
xx