Category: <b>serial I/O</b>
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<pre><b>INT 2F - AVATAR Serial Dispatcher - INSTALL IRQ3 HANDLER</b>

	AX = 1A42h
	BX = 4156h ('AV')
	ES:DI -&gt; FAR handler for serial port using IRQ3
	DS = data segment needed by handler
Return: AX = status/return value
	    0000h if no more room
	    1A42h if ASD not installed
	    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=1A43h,AX=1A62h
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