Method and apparatus for data alignment

DETAILED DESCRIPTION The present invention is a method and apparatus for the synchronization of a receiver located on an F.
sub.
-- port of a Fibre Channel switch with an external N.
sub.
-- port to ensure the reception of transmission characters including four byte ordered sets having a comma character positioned as the left most byte in the ordered set.
The comma character is a special transmission character having a specific 10-bit (byte) character string (a comma character includes either the seven bit sequence "0011111" or "1100000" in bit positions ?9-3!).
An ordered set consists of four bytes of transmission characters in which the left most byte is a comma character.
The receiver is synchronized when it receives a steady stream of transmission characters including at least three ordered sets in a row without any interposed invalid transmission words.
Detection circuity locates comma characters within the data stream and an alignment circuitry shifts their position such that each port receives a regular pattern of comma characters located as the left most byte of an ordered set, and for ensuring that excessive comma characters are masked out.
The detection circuitry further comprises a comma detector for ascertaining the presence of a comma character, a four stage comma bank register and a four stage register bank, wherein, if the comma detector detects the presence of a comma character, a one-bit flag is passed along to the four stage Comma bank register, and the 10-bit transmission character is passed onto the four stage register bank.
The alignment circuitry comprises a comma bank multiplexer for receiving the four outputs of comma bank register, a register bank multiplexer for receiving the four outputs of the register bank, and control logic synchronized by a clock enable generated from a system synchronization pulse, wherein the control logic ascertains whether the F.
sub.
-- port receiver is synchronized with the N.
sub.
-- port.
If the receiver is not synchronized and only one comma character is identified, the control logic provides a datapath select pulse to latch onto the comma bank multiplexer and the register bank multiplexer to select the comma character within the register bank to position it as the left most byte in the ordered set