NEC 78K0 Series User Manual page 557

Here is an example of description of the software for setting the option bytes.
OPT CSEG AT 0080H
OPTION: DB 30H
DB 00H
DB 00H
DB 00H
DB 00H
Remark Referencing of the option byte is performed during reset processing. For the reset processing timing,
see CHAPTER 22 RESET FUNCTION.
CHAPTER 25 OPTION BYTE
; Enables watchdog timer operation (illegal access detection operation),
; Window open period of watchdog timer: 50%,
; Overflow time of watchdog timer: 2
; Internal low-speed oscillator can be stopped by software.
; 1.59 V POC mode
; Reserved area
; Reserved area
; On-chip debug operation disabled
Preliminary User's Manual U17260EJ3V1UD
10
/f ,
RL
557