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"