The M68HC11 Family of MCUs (microcontroller units) has a bootstrap mode that allows a user-defined program to be loaded into the internal random-access memory (RAM) by way of the serial communications interface (SCI); the M68HC11 then executes this loaded program. The loaded program can do anything a normal user program can do as well as anything a factory test program can do because protected control bits are accessible in bootstrap mode. Although the bootstrap mode is a single-chip mode of operation, expanded mode resources are accessible because the mode control bits can be changed while operating in the bootstrap mode.