Scramble codec and a television receiver incorporating the same

Abstract

A scramble codec comprises a latch means for holding an ID number for securing television or other communication data, a pair of memories which can be alternately loaded with input communication data signals in a predetermined cycle, a shift register which is initialized with the ID number held by the latch means to output dissimilar pseudorandom pulse signals in a predetermined cycle, an address setting circuit which sets, as the initial value, a value corresponding to the output of the shift register in scrambling and a value obtainable by subtracting the output of the shift register from the maximum address value of the memories in descrambling, and an address counter which reads communication data from the address designated by the address setting circuit. The above scramble codec has both the function of a decoder for scrambled communication data and the function of an encoder for scrambling communication data, is simple in construction and compact and features improved security. The scramble codec, as such, can be easily built into a receiver such as a television receiver to provide, for example, a television receiver which does not only function as an information receiver but can be used in combination with a VTR or other recording device for the mutual transmission and reception of communication data with security fully retained. Further improvement in security is obtained when the above scramble codec further comprises a nonvolatile key data memory for holding a specified key data and an EOR circuit which takes the exclusive logical sum of the ID number data held by the latch means and the output of the key data memory, with the output of the EOR circuit being set as the initial value in the shift register which outputs dissimilar pseudorandom pulse signals in a predetermined cycle.