Category: no classification

INT 2F - Multiplex - NOTES

	AH = identifier of program which is to handle the interrupt
	   00h-3Fh reserved for IBM (for DOS)
	   40h-7Fh reserved for Microsoft (for DOS)
	   80h-B7h reserved for IBM
	   B8h-BFh reserved for networks
	   C0h-FFh reserved for applications
	AL is the function code
   This is a general mechanism for verifying the presence of a TSR and
   communicating with it.  When searching for a free identifier code for AH
   using the installation check (AL=00h), the calling program should set
   BX/CX/DX to 0000h and must not depend on any registers other than CS:IP
   and SS:SP to be valid on return, since numerous programs now use additional
   registers on input and/or output for the installation check.
Notes:	Since the multiplex chain is growing so long, and beginning to
	  experience multiplex number collisions, I have proposed an alternate
	  multiplex interrupt on INT 2D.  If you decide to use the alternate
	  multiplex, please let me know.
	DOS and some other programs return values in the flags register, so
	  any TSR which chains by calling the previous handler rather than
	  jumping to it should ensure that the returned flags are preserved
	  and passed back to the original caller