System having input output pins shifting between programming mode and normal mode to program memory without dedicating input output pins for programming mode

A programmable semiconductor microcontroller chip for installing into and to control an electrically operated system, comprising:

• a plurality of input/output (I/O) pins for receiving instruction words and data entered in the form of electrical signals to be processed by the microcontroller chip, the total number of said I/O pins is less than the number of bits in an instruction word,
• an on-chip programmable memory adapted to be programmed by instruction words received as inputs to the microcontroller chip at the (I/O) pins, means for selectively implementing electrical isolation of at least some of the I/O pins from the system to be controlled by the microcontroller chip, to suppress disturbances to the system when the memory is being programmed with the microcontroller chip installed in the system;
• and
• interface means for selectively responding to instruction words entered via at least some of said I/O pins in either serial or parallel fashion to program the programmable memory wherein said at least some of said I/O pins are dual function for shifting the chip between a programming mode and a normal mode, such that during said programming mode said at least some of said I/O pins are used to program said on-chip programming memory and during said normal mode said at least some of said I/O pins are used for inputting and outputting data appropriate for implementing control of the system in which the microcontroller chip is installed, thereby eliminating the need for dedicated programming I/O pins.

A method of programming a programmable microcontroller for installing into and for controlling an electrically operated system, while the microcontroller is installed within the system, the microcontroller having a plurality of input ports, the method comprising the steps of:

• selecting at least some of the input ports for performing a dual function according to whether the microcontroller is operating in a normal mode or a programming mode and thereby eliminating the need for dedicated programming pins,
• using said at least some of the input ports for receiving instruction words to be entered in the microcontroller while in said normal mode, the number of input ports being smaller than the number of bits in an instruction word
• using said at least some of the input ports for receiving data serially to be used to program the microcontroller while in said program mode;
• and,
• substantially isolating electrical levels associated with programming the microcontroller from the circuit of the system to be controlled, with the microcontroller installed in circuit with the system, to preclude disturbances to the system during the in-system programming.