Method of rewriting program in a flash microcomputer

A method of writing a new boot program into a memory device having first and second memory blocks into which a boot program can be written and from which a boot program can be read, the first memory block being identified as a primary boot block storing an existing boot program and the second memory block being a secondary block storing other information, the method comprising the steps of:

• erasing the second memory block;
• writing the new boot program into the erased second memory block;
• after writing the new boot program, changing an identity of the primary boot block from the first memory block to the second memory block;
• erasing the first memory block;
• storing other information in the first memory block;
• retaining the identity of the primary boot block as the second memory block until a further new boot program is written into the memory device;
• and
• wherein the step changing an identity of the primary boot block comprises the steps of storing in a storage area associated with the first memory block first program data indicating that the first memory block stores an existing boot program, storing in a storage area associated with the second memory block second program data different from the first program data indicating that the second memory block stores a new boot program, and exchanging addresses of the second memory block and the first memory block.