NXP Semiconductors MC9S08SU16 Reference Manual page 547

Chapter 27 Development support
BDC_SBDFR field descriptions (continued)
Field Description
A serial active background mode command such as WRITE_BYTE allows an external debug host to force
a target system reset. Writing 1 to this bit forces an MCU reset. This bit cannot be written from a user
program.
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
NXP Semiconductors 547