Abstract: A procedure and processor are disclosed for avoiding lengthy delays in debug procedures during access by a memory mapped peripheral device. The processor includes in-circuit emulation means comprising one or more scan chains or serially connected registers for access by an external host computer system. The procedure comprises: a) the host computer system carrying out a debug procedure via said scan chains, and selectively interrupting such debug procedure for access to a peripheral memory mapped device; b) the host computer system writing into an area or memory of the processor a program for reading and/or writing data at a specified memory location; and c) the host computer system causing said processor to run said program, and then to return to said debug procedure.