Patent ID: 8601251

Claim:
A single-chip semiconductor integrated circuit comprising: a standby microcomputer which receives power supply from a first power source; a main microcomputer which receives power supply from a second power source independent from the first power source; and a block circuit which blocks a signal input from said standby microcomputer to said main microcomputer when the first power source is switched ON and the second power source is switched OFF, wherein said standby microcomputer includes: a first Read Only Memory (ROM) which stores a first boot program; and a first processing unit configured to execute the first boot program, said main microcomputer includes: a second ROM which stores a second boot program; and a second processing unit configured to execute the second boot program, said first processing unit is configured to execute the first boot program when the first power source is switched ON so as to switch ON the second power source and to load the first program from an external nonvolatile memory, and to execute the loaded first program, and said second processing unit is configured to execute the second boot program when the second power source is switched ON so as to load the second program from the external nonvolatile memory, and to execute the loaded second program.