Drive circuitry with error detection and compensating threshold arrangement

Claim 1

Apparatus for transmitting signals along a plurality of paths and for determining whether or not signals are being transmitted on a predetermined number of the paths, said apparatus including in combination a plurality of signal paths, each signal path including an input terminal adapted to receive input signal data, an output terminal, and a driving means having an input connection coupled to said input terminal and an output connection coupled to said output terminal; additional driving means having an input connection and an output connection; activating means coupled to the driving means of the plurality and to the additional driving means for applying operating potentials to the driving means; each of said driving means being operable to produce a first output voltage at its output connection in response to a first input condition at its input connection, and being operable to produce a second output voltage at its output connection in response to a second input condition at its input connection when operating potentials are applied thereto by the activating means; a resistance network comprising an equal plurality of resistances, each resistance having one end connected to the output connection of a different one of the driving means of said plurality and the other end connected to a common juncture, the voltage level produced at the common juncture being proportional to the number of output connections having said first output voltage present thereon; first comparator means having a first and a second input, the first input being connected to said common juncture; first threshold setting means connected to the output connection of said additional driving means and to the second input of the first comparator means, said first threshold setting means being operable to produce a voltage at the second input to the first comparator means which is less than the voltage produced at the first input to the first comparator means when a predetermined number (N) of output connections of the driving means of said plurality have said first output voltage present thereon and greater than the voltage produced at the first input to the first comparator means when said predetermined number minus one (N- 1) of output connections of the driving means of said plurality have said first output voltage present thereon; said first comparator means being operable to produce a first output signal when the voltage at its first input is less than that at its second input and to produce a second output signal when the voltage at its first input is more than that at its second input; second comparator means having a first and a second input, the first input being connected to said common juncture; second threshold setting means connected to the output connection of said additional driving means and to the second input of thesecond comparator means, said second threshold setting means being operable to produce a voltage at the second input to the second comparator means which is less than the voltage produced at the first input of the second comparator means when said predetermined number plus one (N + 1) output connections of the driving means of said plurality have said first output voltage present thereon and greater than the voltage produced at the first input to the second comparator means when said predetermined number (N) of output connections of the driving means of said plurality have said first output voltage present thereon; said second comparator means being operable to produce a first output signal when the voltage at its first input is less than that at its second input and to produce a second output signal when the voltage at its first input is more than that at its second input; and output means coupled to said first and second comparator means for producing an error signal in response to a first output signal from the first comparator means or a second output signal from the second comparator means.