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Boundary Acquisition on a Serial BIT to Parallel Byte Conversion

IP.com Disclosure Number: IPCOM000035721D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Jenkins, RB: AUTHOR

Abstract

A method for acquiring the boundary of a parallel byte to data upon its conversion from a serial stream of data bits is described in this article.

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Boundary Acquisition on a Serial BIT to Parallel Byte Conversion

A method for acquiring the boundary of a parallel byte to data upon its conversion from a serial stream of data bits is described in this article.

Fig. 1 shows a typical dataflow for converting a serial stream of data bits into a parallel byte of data. In such a conversion, some device must be used to insure that the boundary of the parallel byte is in proper alignment.

Fig. 1 also shows the generation of a byte clock which will be used in processing each parallel byte after its conversion from a serial dataflow. This clock may be generated by several means, but its byte frequency must be a specific fraction of the bit frequency of the serial bit stream. In this example, the byte clock frequency is a tenth of the bit frequency because there are 10 bits in each byte. As the bits enter serially, a 10-bit-wide byte will be formulated in each cycle of the byte clock.

Once in a parallel format, the bytes are checked for proper alignment. In order to determine if the boundary is in error, the 10-bit- wide parallel byte could be predefined as having only specific values. In this design, the 8-bit bytes were encoded into 10-bit bytes before serial transmission. The 10-bit byte will be decoded later in this dataflow back into 8 bits, of which all 256 combinations will be allowed. Only certain combinations of the 10 bits are allowed, however. When the parallel byte received does not match one of these combinations, an error is flagged for that byte.

Fig. 2 shows the use of an error indicator in the dataflow that can be used to help reacquire the proper byte boundary. It is not necessary to assume that if a byte is in error the byte is misaligned. The error indicator dev...