Computer control system for selecting a desired control program from a plurality of control programs

In a control device for an elevator system comprising a central processing unit, a first read-only memory for storing a first set of program instructions for computing output control signals for operating controlling means of said elevator system in response to input instructing signals to said central processing unit, an output circuit for communicating said output control signals to said controlling means, a first random access memory for storing said output control signals produced as a result of execution of said first set of program instructions immediately prior to said output control signals being communicated to said controlling means by said output circuit, and address and data buses for connecting said first read-only memory, said output circuit, and said first random access memory with said central processing means, the improvement comprising:

• a second read-only memory and a second random access memory, said second read-only memory and said second random access memory being connected to said central processing means by said address and data buses, said second read-only memory containing a second set of program instructions for selectively modifying said output control signals produced as a result of said first set of program instructions.