IBM PC CONVERTIBLE Technical Reference page 209

0321
SYS_MOD_OFF:
0321 BB 0002 MOV BX ,0002H SELECT MODEM
0324 E8 0000 E CALL
COM_POWER AND TURN OFF
0327
SYSjlOD_END:
0327 2A CO SUB AL,AL
RETURN WIO ERROR
0329 SYS_MOD_EX IT:
0329 C3
RET
032A
SYSjlODEM_PWR
ENDP
2-184 ROM BIOS