Externally reprogrammable vehicular microcomputer with hardware lock-out of unauthorized memory modifications

An externally reprogrammable computer system, responsive to an external programming unit (P,1), for an automotive vehicle (5) having a control unit (2) including

• a microprocessor or computer (23);
• a non-volatile, read-only programmable memory (EEPROM) (25) permanently connected to the computer (23) and addressed by the computer for entry of data into the memory and for retrieval of data from the memory for carrying out computation operations by the computer,
• means (24) interconnecting said microprocessor and memory;
• means (26) transmitting operating data from the vehicle to the computer (23);
• means (27) for transmitting computed data from the computer to the vehicle, for controlling vehicle operations in accordance with the computed data,
• the computer receiving the operating data and computing the control data based on the received operating data and on data stored in said memory (25),
• comprising
• reprogramming authorization and transmission means (13,11,12,21,22) including
• an interface (3, 11, 12) connecting the external programming unit (1) to the microprocessor (23) in the control unit (2) and signaling said programming unit when data have been accurately transmitted over the interface;
• means in said memory (25) making said memory normally non-responsive to writing instructions from said microprocessor and to any stray voltages on said means (24) interconnecting said microprocessor and memory;
• and
• a release-enable bus (13) coupled from said external programming unit (1) through said interface to the memory (25) and authorizing writing of new program data into the memory only when said external programming unit has received from said interface (3) an "accurate transmission" signal.