Altera Stratix GX Transceiver - Manual (Page 86)

4–4 Altera Corporation
Stratix GX Transceiver User Guide January 2005
SONET Mode Receiver Architecture
Manual SONET Alignment Mode (2 Consecutive 8-bit Characters
(A1A2) or 4 Consecutive 8-bit Characters (A1A1A2A2)
The 2 consecutive 8-bit characters, A1A2 SONET Section Overhead
Framing Bytes, are used as the comma in 16-bit pattern mode.
The 16-bit comma is specified in the MegaWizard Plug-In Manager. The
comma has the bit orientation of [MSB..LSB]. A1 represents the least
significant byte, which consist of bits [7..0], and A2 represents the most
significant byte consisting of bits [15..8]. The comma, or alignment
pattern, must be specified as [A2,A1] in the MegaWizard Plug-In
Manager. If “Flip Word Alignment bits” is selected, the ordering of the
alignment pattern is [LSB..MSB] for the bit ordering and [A1, A2] for the
byte ordering. Only the positive disparity of the comma is detected in the
mode.
Table 4–1 shows several word alignment patterns based on
different bit transmission orders and whether the receiver word
alignment bit flip option is checked. The bit transmission order assumes
that if double width mode is used, the LSB is transmitted first, followed
by the MSB.
In SONET mode, the word aligner either aligns to two consecutive 8-bit
characters (A1A2) or four consecutive 8-bit characters (A1A1A2A2). The
rx_a1a2size[]
signal differentiates between the 2 and 4 consecutive
modes. The word aligner aligns to the A1A2 pattern when the
rx_a1a2size[]
is held low, or to the A1A1A2A2 when
rx_a1a2size[] is high. If the optional rx_a1a2size signal is not
selected, the word aligner defaults to the A1A2 mode. An optional signal,
rx_a1a2sizeout[]
, can also be enabled to send the state of the
rx_a1a2[] signal as seen by the word aligner into the device logic array.
The value of the signal is forwarded to the device, along with the byte that
was in the word aligner when the rx_a1a2size[] signal was sampled.
Table 4–1. Word Alignment Patterns for SONET Mode
Bit Transmission Order
(at the Source)
Word Alignment Bit Flip Word Alignment Pattern
MSB to LSB On 1111011000101000
(hex F628)
MSB to LSB Off 0001010001101111
(hex 146F)
LSB to MSB Off 0010100011110110
(hex 28F6)