64B/66B; Encoder; Table 2-10: 64B/66B Bypassing; Table 2-11: Transmit 64B/66B Encoder Control Mapping - Xilinx RocketIO X User Manual

Block Level Functions

64B/66B

Encoder

Bypassing
There are two types of bypassing regarding the 64B/66B encoder. The encoder block can
either be entirely bypassed, or the 64B/66B encoder can be used and can be bypassed on a
clock-by-clock basis.
If TXENC64B66BUSE is deasserted Low, the entire 64B/66B encoder is not used. If
encoding is done in the fabric, the sync header [0:1] must be placed at
TXCHARDISPVAL[0] and TXCHARDISPMODE[0] with the 32 TXDATA bits.
If TXENC64B66BUSE is asserted High, the TXBYPASS8B10B bit 0 signal bypasses the
64B/66B encoder on a clock basis, which means that two clock cycles are needed to do a full
bypass of a block. The Sync Header is taken from the TXCHARDISPMODE[0:1]. To bypass
on a block basis, the even boundary needs to be indicated at the fabric interface, which is
contained in TXKERR bit 0. The TXCHARISK signal performs the function of TXC.

Table 2-10: 64B/66B Bypassing

The transmit 64B/66B encoder borrows four bits of the TXCHARISK bus (bits [3:0]) to convey
the control signaling to the 64B/66B encoder. The four TXC bits track with the four bytes of
TXDATA_IN (TXC[0] with TXDATA_IN[7:0], and so on) to signal data block formatting. The
transmit fabric interface logic (which first monitors transmit data as it travels from the fabric
interface to the PMA) drives the encoder with the four TXC bits as follows:

Table 2-11: Transmit 64B/66B Encoder Control Mapping

RocketIO™ X Transceiver User Guide
UG035 (v1.5) November 22, 2004
Signal
TXENC64B66BUSE
TXBYPASS8B10B[0]
TXCHARDISPMODE[0:1]
TXKERR[3]
TXCHARISK[3:0]
Notes:
1. TX sync header [0] = TXCHARDISPMODE[0]
TX sync header [1] = TXCHARDISPVAL[0]
TXC[3:0] (TXCHARISK[3:0])
1111
0001
1110
1100
0 entire 64B/66B encoder bypassed
1 bypass on a clock-to-clock basis
Function 64B/66B clock-to-clock
bypass
0 indicates no bypass
1 indicates bypass this block
sync header shown in Figure 2-9
(same as SH[0:1])
indicates even boundary for
bypassing on block basis
performs function of TXC
Idles OR terminate-with-idles
Start-of-frame OR ordered-set
Terminate in second position
Terminate in third position
www.xilinx.com
1-800-255-7778
Function
Function 64B/66B entirely
bypassed
defined by Table 2-12
indicates which byte contains the
sync header
indicates character is a (K)
control character
Block Formatting
R
(1)
57