The ROM of the PC-G850 has the following code that supports automatic start, and it seems that if there is a character string set to 0x40- at startup, it will jump to address 0x50.
// AUTO RUN System of PC-G850V
// if Magic Word -
// 0x0040 : "MACHINE LANGUAGE",
// 0x0050 : 0xC3
// Found @ 0x0040 , JP 0x0050
C3BE : 11 40 00 ld de,0x0040 ; Magic Word Address
C3C1 : CD C9 C3 call 0xC3C9 ;
C3C4 : D0 ret nc ;
C3C5 : F1 pop af ;
C3C6 : C3 50 00 jp 0x0050 ; if Found, JP 0x0050
C3C9 : 21 DA C3 ld hl,0xC3DA ; "MACHINE LANGUAGE",0xC3
C3CC : 06 11 ld b,0x11 ; LEN=17
C3CE : 1A ld a,(de) ;
C3CF : BE cp (hl) ;
C3D0 : 20 06 jr nz,0xC3D8 ;
C3D2 : 13 inc de ;
C3D3 : 23 inc hl ;
C3D4 : 10 F8 djnz 0xC3CE ;
C3D6 : 37 scf ;
C3D7 : C9 ret ;
C3D8 : A7 and a ;
C3D9 : C9 ret ;
; Magic Word Table
C3DA : 4D 41 43 48 49 4E 45 20 4C 41 4E 47 55 41 47 45 : MACHINE.LANGUAGE
C3EA : C3