10. An input stage according to claim 8, further characterized by said comparison means being operable to produce an output signal identifying the received address signal symbol as an end terminal signal representing the end of an address signal, and means responsive to the 1 condition of said spacer signal bistable means and the 1 condition of said keyword character bistable means to reset both said spacer signal and keyword character bistable means to the 0 condition and to generate an acceptance signal representing acceptance of the address signal upon the occurrence of the end terminal signal identifying output signal.
8. An input stage according to claim 2, further characterized by said comparison means operable to receive the address signal, symbol by symbol, and to generate output signals respectively identifying the keyword character signals, the spacer signal, the terminal signal, and an unacceptable symbol signal, a plurality of bistable means to be selectively switched to a 1 or to an 0 stable condition including a keyword character bistable means responsive to a keyword character identifying output signal to change its state from the 0 to the 1 condition, a spacer signal bistable means responsive to a spacer signal identifying output signal to change its state from the 0 to the 1 condition, a terminal signal bistable means responsive to a terminal signal identifying output signal to change its state from the 0 to the 1 condition, said comparison means including means responsive to the 1 condition of said keyword character bistable means and the 0 condition of said spacer signal bistable means to change the state of the spacer signal bistable means to the 1 condition, reset or maintain said terminal signal bistable means in the 0 condition and reset said keyword character bistable means to the 0 condition upon the occurrence of a spacer signal identifying output signal, and means responsive to the 1 condition of said keyword character bistable means, the 1 condition of said spacer signal bistable means and the 0 condition of said terminal signal bistable means to change the state of said terminal signal bistable means to the 1 condition, reset said spacer signal bistable means to the 0 condition and reset said keyword character bistable means to the 0 condition upon the occurrence of a terminal signal identifying output signal.