Altera Stratix GX Transceiver - Manual (Page 65)

Altera Corporation 3–19
January 2005 Stratix GX Transceiver User Guide
Basic Mode
Figure 3–17 shows the reset behavior of the 8B/10B encoder. When in
reset (txdigitalreset is high), a K28.5- (K28.5 10-bit code from the
RD- column) is sent continuously until txdigitalreset is low. Because
of the pipelining of the transmitter channel, there are some don't-care
values (10'hxxx) until the first of three K28.5 is sent (
Figure 3–17 shows
three don't-cares). Normal user data follows the third K28.5.
Figure 3–17. Transmitter Output During Reset Conditions
Control Code Encoding
The tx_ctrlenable[] controls when a control code is to be inserted in
the encoded data flow. When tx_ctrlenable[] is low, the byte at
tx_in[]
is encoded as data. When tx_ctrlenable[] is high,
tx_in[] is encoded as a control word. Figure 3–18 shows that the
second 0xBC is encoded as a control code. The others are encoded as data.
Figure 3–18. Control Word Identification Waveform
The 8B/10B encoder does not check whether the control code word
entered is one of the 12 valid control code-groups. If an invalid control
code is entered, the resulting 10-bit code might also be invalid (might not
map to a valid Dx.y or Kx.y code), depending on the value entered.
clock
tx_out[9:0 ]
txdigitalreset
K28.5- K28.5- K28.5- xxx xxx xxx K28.5- k28.5+ K28.5- Dx.y+
clock
tx_in[7:0]
tx_ctrlenable
83 78 BC BC 0F 00 BF 3C
D3.4 D24.3 D28.5 K28.5 D15.0 D0.0 D31.5 D28.1 Code Group