INT 21 - Phar Lap 386/DOS-Extender - SET PROTECTED-MODE INTERRUPT VECTOR
AX = 2504h
CL = interrupt number
DS:EDX = CS:EIP of protected-mode interrupt handler
Return: CF clear
Note:   this function is also supported by FlashTek X-32VM
SeeAlso: AX=2505h,INT 31/AX=0205h

See also: 212502

212504 - Phar Lap 386/DOS-Extender - SET PROTECTED-MODE INTERRUPT VECTOR