Controlled machine inhibition when control module is absent

In a programmable control system having a main control program and provision for adding memory modules containing additional control programs to operate a controlled machine, said control system including a plurality of output means for supplying control signals to said controlled machine, a plurality of input means for receiving signals, activation means for enabling said controlled machine to be operated, said activation means being coupled to a particular one of said plurality of output means, and add-on memory module means for storing an additional control program, the improvement comprising:

• means for supplying a signal in response to said main control program to a certain one of said plurality of output means, said signal being indicative of activating said activation means;
• means for coupling said certain one of said plurality of output means to a certain one of said plurality of input means;
• means responsive to said additional control program for sensing said certain one of said plurality of input means;
• and
• means responsive to said additional control program and the value of said sensed certain one of said plurality of input means for supplying an activation signal to said activation means via said particular one of said output means.

A method for activating an external device by a system under the control of first and second programs, said system including a plurality of output means for supplying signals and a plurality of input means for receiving signals, comprising the steps of:

• supplying a first activating signal to a first one of said output means in response to said first program;
• coupling said first one of said output means to one of said input means;
• sensing said first activating signal at said one of said input means in response to said second program;
• supplying a second activation signal to a second one of said output means in response to sensing said first activation signal;
• and
• conducting said second activation signal to said external device.

In a programmed controller means for generating control signals to control a controlled device, at least one of said control signals being necessary to the operation of the controlled device, the controller means including output means for supplying said control signals from said controller means and for coupling at least some of said control signals to said controlled device, and input means for coupling input signals to said controller means, the improvement comprising:

• means for coupling at least one of said necessary control signals from said output means to said input means and not to said controlled device;
• add-on means, removably attachable to and forming part of said controller means, for supplying essential control signals to said controlled device;
• and
• means, in said add-on means, for sensing the presence of at least one of said necessary control signals at said input means and for supplying said sensed necessary control signal to said output means to be coupled to said controlled device.

A method, in a system for controlling a controlled device, for coupling a necessary control signal to said controlled device only if a subroutine, essential to the control of said controlled device, is available, comprising the steps of:

• causing a signal, representative of a necessary control signal, to be coupled to set an output latching means;
• coupling said output latching means to an input means;
• and
• calling an essential subroutine which includes the steps of:
• sensing said input means to determine whether said output latching means is set, and
• supplying said necessary signal to said controlled device only if said output latching means is set.