HC4GX15 Datasheet, PDF (308/668 Pages) Altera Corporation – HardCopy IV Device Handbook

1–44
Chapter 1: HardCopy IV GX Transceiver Architecture
Transmitter Channel Datapath
In double-width mode, the cascaded 8B/10B encoder generates two 10-bit code
groups from two 8-bit data and their respective control code identifiers. Figure 1–30
shows the conversion format. The LSB shown in Figure 1–30 is transmitted first.
Figure 1–30. 8B/10B Conversion Format in Double-Width Mode
CTRL[1:0]
H ' G' F' E' D ' C ' B' A' H G F E D C B A
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Parallel Data
Cascaded 8B/10B Conversion
j' h ' g ' f ' i' e ' d ' c ' b ' a ' j h g f i e d c b a
19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
MSB
LSB
Control Code Encoding
In double-width mode, the tx_ctrlenable[1:0] port is used to identify which
8-bit data is to be encoded as a control word. The lower bit, tx_ctrlenable[0], is
associated with the LSByte; the upper bit, tx_ctrlenable[1], 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 1–31 shows that only the lower byte of the tx_datain[15:0] port is encoded
as a control code because tx_ctrlenable[0] is high in the second clock cycle.
Figure 1–31. Encoded Control Word and Data Word Transmission
clock
tx_datain[15:0]
tx_ctrlenable[1:0]
8378
0
BCBC
1
0F00
0
BF3C
code group
D3.4
D24.3
D28.5
K28.5
D15.0
D0.0
D31.5
D28.1
The 8B/10B encoder does not check to see if the code word entered is one of the 12
valid control code groups specified in the IEEE 802.3 8B/10B encoder specification. If
an invalid control code is entered, the resulting 10-bit code may be encoded 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.
HardCopy IV Device Handbook Volume 3
© June 2009 Altera Corporation