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 SeeAlso: INT 2D"ALTERNATE MULTIPLEX"