INT 2F - AVATAR Serial Dispatcher - INSTALL IRQ4 HANDLER
AX = 1A43h
BX = 4156h ('AV')
ES:DI -> FAR handler for serial port using IRQ4
DS = data segment needed by handler
Return: AX = 1A43h if ASD not installed
= 0000h if no more room
else handle to use when uninstalling
Notes:  (see AX=1A42h)
SeeAlso: AX=1A63h

See also: 2F1A42

2F1A43BX4156 - AVATAR Serial Dispatcher - INSTALL IRQ4 HANDLER