commence also shown coupled to the output of or gate 24 is a one shot or monostable multivibrator 26 the function of the multivibrator 26 is to reset the timer each time a switch is depressed for a shorter period such as for example when a user is punching in the secret code the one shot 26 is responsive to for example the trailing edge of a key activation as for example when a key is depressed and then released in this manner the one shot 26 will continuously reset the timer during normal keyboard operation when the hold down function is desired the user is required to hold down a key indicative of a test procedure for a predetermined interval determined by the timing interval provided by the timer 25 each key as 20 and 21 is also associated with an and gate as gates 28 and 29 where the output of the and gate is associated with a separate flip flop as flip flops 30 and 31 as will be explained the function of the flip flops 30 and 31 is to implement a different test mode when a key has been actuated for the predetermined time interval the output of the timer 25 has one lead coupled to the input of a one shot or monostable multivibrator 32 the output of the multivibrator 32 is directed to suitable inputs of and gates 28 and 29 which as will be explained activate the associated flip flops as 30 and 31 for the depression of keys 20 and 21.