Altera Corporation
2–39
October 2007
Stratix II GX Device Handbook, Volume 2
Stratix II GX Transceiver Architecture Overview
Figure 2–32. Transmitter Output During Reset Conditions
Control Code Encoding
The
tx_ctrlenable
port identifies which 8-bit data is encoded as a
control word. If this port is not used, control words cannot be sent. In
double-width mode, the
tx_ctrlenable
port has two bits. The lower
bit is associated with the LSByte and the upper bit is associated with the
MSByte. When
tx_ctrlenable
is low, the byte at the
tx_datain
port
of the transceiver is encoded as data (Dx.y), otherwise, it is encoded as a
control code (Kx.y).
Figure 2–33
shows that the lower byte of the second
byte of
tx_datain
(8’hBC) is encoded as a control code as identified by
a high on the lower
tx_ctrlenable
bit’s second clock cycle.
Figure 2–33. Control Word Identification Waveform
The 8B/10B encoder does not check to see if the code word entered is one
of the 12 valid codes. If an invalid control code is entered, the resultant
10-bit code may be encoded as an invalid code (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 an 8B/10B decoder to decode an invalid control word
encoded into a valid Dx.y code without asserting any code error flags. For
example, depending on the current running disparity, the invalid code
clock
dataout[19..10 ]
tx_digitalreset
K28.5-
K28.5-
K28.5-
xxx
xxx
xxx
K28.5+
k28.5+
K28.5+
Dx.y+
dataout[9..0 ]
K28.5+
K28.5+ K28.5+
xxx
xxx
xxx
K28.5-
k28.5-
K28.5-
Dx.y-
clock
tx_datain[15..0]
tx_ctrlenable[1..0]
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
0
1
0