Device for exception processing procedure in software control of processor and its operation method

The device is used for changing over in operation among a user mode, an exception prior period mode and an exception mode. In case of some exception, the processor exeuctes one exception setting and initiating procedure before executing the exception program. During the setting and before jumping to the starting procedure, the present mode and return address are stored in the buffer. during the initiation, the programmer is allowed to select storing information or debugging value before changing over registers. Thus the programmer obtains great flexibility in software debugging and creating exception program.