HC4GX15 Datasheet, PDF (378/668 Pages) Altera Corporation – HardCopy IV Device Handbook

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Chapter 1: HardCopy IV GX Transceiver Architecture
Receiver Channel Datapath
Figure 1–97 shows an example of the byte ordering operation in single-width modes.
In this example, A is the programmed byte ordering pattern and PAD is the
programmed PAD pattern. The byte deserialized data places the byte ordering pattern
A in the MSByte position, resulting in incorrect byte ordering. Assuming that a rising
edge on the rx_syncstatus signal had occurred before the byte ordering block sees
the byte ordering pattern A in the MSByte position, the byte ordering block inserts a
PAD byte and pushes the byte ordering pattern A in the LSByte position. The data at
the output of the byte ordering block has correct byte ordering as reflected on the
rx_byteorderalignstatus signal.
Figure 1–97. Byte Ordering in Single-Width Modes
Transmitter
Channel
Receiver
tx_datain[15:8] D2 D3 D5
tx_datain[7:0] D1 ^A D4
Byte
Serializer
Byte
Deserializer
D1 A D4
xx D2 D3
Byte
Ordering
D1 PAD D3 D5 rx_dataout[15:8]
xx D2 A D4 ^{rx_dataout[7:0]}
rx_byteorderalignstatus
If the byte ordering block sees another rising edge on the rx_syncstatus signal
from the word aligner, it de-asserts the rx_byteorderalignstatus signal and
repeats the byte ordering operation as previously described.
User-Controlled Byte Ordering
Unlike word-alignment-based byte ordering, user-controlled byte ordering provides
control to the user logic to restore correct byte ordering at the receiver. When enabled,
an rx_enabyteord port is available that you can use to trigger the byte ordering
operation. A rising edge on the rx_enabyteord port triggers the byte ordering
block. After a rising edge on the rx_enabyteord signal, if the byte ordering block
finds the first data byte that matches the programmed byte ordering pattern in the
MSByte position of the byte-deserialized data, it inserts one programmed PAD
pattern to push the byte ordering pattern in the LSByte position. If the byte ordering
blocks finds the first data byte that matches the programmed byte ordering pattern in
the LSByte position of the byte-deserialized data, it considers the data to be byte
ordered and does not insert any PAD byte. In either case, the byte ordering block
asserts the rx_byteorderalignstatus signal.
HardCopy IV Device Handbook Volume 3
© June 2009 Altera Corporation