Frame detection system

Claim 1

In a digital communications system wherein data is serially transmitted in frames of multi-bit bytes at a fixed clock rate and framing is defined by a framing pattern at the start of each frame, the framing pattern comprising a predetermined number of bytes of a first digital pattern followed by said predetermined number of bytes of a second digital pattern, an arrangement for detecting said framing pattern in transmitted data and providing a frame signal when said framing pattern is detected comprising: clock means for providing clock pulses at said fixed clock rate; means for receiving said data; first detection means for examining the received data bits and providing a first signal when N sequentially received data bits form said first digital pattern, where N is an integral number equal to the number of bits in a byte; second detection means for examining the received data bits and providing a second signal when N sequentially received data bits form said second digital pattern; first counter means responsive to the occurrence of said first signal for incrementing an internal count; means responsive to the internal count of said first counter means reaching said predetermined number for providing an enabling signal; second counter means enabled by said enabling signal for incrementing an internal count in response to the occurrence of said second signal; reset means utilizing said clock pulses and responsive to a first occurrence of said first signal or said second signal for resetting the internal counts of said first and second counter means in the event there is not another occurrence of said first signal or said second signal after N clock pulses; and output means responsive to the internal count of said second counter means reaching said predetermined number after the internal count of said first counter means reached said predetermined number for generating said frame signal.