INT 2F - AVATAR Serial Dispatcher - INSTALL IRQ3 HANDLER
AX = 1A42h
BX = 4156h ('AV')
ES:DI -> FAR handler for serial port using IRQ3
DS = data segment needed by handler
Return: AX = 1A42h if ASD not installed
= 0000h if no more room
else handle to use when uninstalling
Notes:  the handler need not save/restore registers or signal EOI to the
interrupt controller
the handler should return AX=0000h if the interrupt was meant for it,
and either leave AX unchanged or return a non-zero value otherwise
the most recently installed handler will be called first, continuing
to earlier handlers until one returns AX=0000h
SeeAlso: AX=1A62h

See also: 2F1A43

2F1A42BX4156 - AVATAR Serial Dispatcher - INSTALL IRQ3 HANDLER