Microcomputer having CPU and built-in flash memory that is rewritable under control of the CPU analyzing a command supplied from an external device

A microcomputer on a semiconductor substrate comprising:

• a flash memory including a plurality of electrically rewritable nonvolatile memory cells and storing a command analyzing program and a control program;
• first external terminals receiving mode signals which represent one of a plurality of operation modes of said microcomputer, said plurality of operation modes including an external write mode for said flash memory;
• a mode control circuit coupled to said first external terminals and setting an operation mode of said microcomputer into said external write mode when the mode signals are indicative of said external write mode;
• a random access memory storing the command analyzing program and the control program provided from said flash memory during said external write mode;
• second external terminals to which one of a plurality of commands is to be supplied from outside of said microcomputer during said external write mode;
• and
• a central processing unit coupled to receive said one command when said microcomputer is in said external write mode and decoding said one command by executing the command analyzing program in said random access memory so as to determine a process to be performed to said flash memory, said central processing unit being responsive to the decoding result of said one command and controlling operations of said flash memory by executing the control program in said random access memory for performing the process, which process is for changing threshold voltages of predetermined memory cells to predetermined threshold voltages or for verifying whether or not the threshold voltages of predetermined memory cells have been changed to predetermined threshold voltages.

A microcomputer on a semiconductor substrate comprising:

• a flash memory including a plurality of electrically rewritable nonvolatile memory cells;
• first external terminals receiving mode signals which represent one of a plurality of operation modes of said microcomputer, said plurality of operation modes including at least an external write mode and an internal write mode for said flash memory;
• a mode control circuit coupled to said first external terminals and setting an operation mode of said microcomputer into said external write mode when the mode signals are indicative of said external write mode and setting an operation mode of said microcomputer into said internal write mode when the mode control signals are indicative of said internal write mode;
• second external terminals to which one of a plurality of commands is to be supplied from outside of said microcomputer during said external write mode;
• and
• a central processing unit,
• wherein said central processing unit is coupled to receive said one command during said external write mode and decodes said one command by executing a command analyzing program so as to determine a process to be performed to said flash memory and is responsive to the decoding result of said one command and controls operations of said flash memory by executing a control program for performing the process, which process is for changing threshold voltages of predetermined memory cells to predetermined threshold voltages or for verifying whether or not the threshold voltages of predetermined memory cells have been changed to predetermined threshold voltages, and
• wherein said central processing unit controls operations of said flash memory during said internal write mode by executing a rewrite sequence control program to rewrite data stored in said flash memory.