File buffers are flushed and any open handles for files or devices owned by the process are closed.Terminates execution of the currently executing program, but reserves part or all of its memory so that it will not be overlaid by the next transient program to be loaded. MS-DOS then takes the following actions:
File buffers are flushed and any open handles for files or devices owned by the process are closed.
The termination handler vector (Int 22H) is restored from PSP:000AH.
The Ctrl-C handler vector (Int 23H) is restored from PSP:000EH.
[2.0+] The critical-error handler vector (Int 24H) is restored from PSP:0012H.
Control is transferred to the termination handler.
If the program is returning to COMMAND.COM, control transfers to the resident portion and the transient portion is reloaded if necessary. If a batch file is in progress, the next line of the file is fetched and interpreted; otherwise a prompt is issued for the next user command.
Call with:
DX = offset of the last byte plus one (relative to the program
segment prefix)
of program to be protected
CS = segment of program segment prefix
Returns:
Nothing
Notes:
This function call is typically used to allow user-written utilities, drivers, or interrupt handlers to be loaded as ordinary .COM or .EXE programs, then remain resident. Subsequent entrance to the code is via a hardware or software interrupt.
This function attempts to set the initial memory allocation block to the length in bytes specified in register DX. If other memory blocks have been requested by the application via Int 21H Function 48H, they will not be released by this function.
Other methods of performing a final exit are:
Int 20H
Int 21H Function 00H
Int 21H Function 31H
Int 21H Function 4CH
This function should not be called by .EXE programs that are loaded at the high end of the transient program area (i.e., linked with the /HIGH switch), because doing so reserves the memory normally used by the transient part of COMMAND.COM. If COMMAND.COM cannot be reloaded, the system will fail.
This function does not work correctly when DX contains values in the range 0FFF1H—0FFFFH. In this case, MS-DOS discards the high bit of the value in DX, resulting in the reservation of 32 KB less memory than was requested by the program.
[2.0+] Int 21H Function 31H should be used in preference to this function, because it supports return codes, allows larger amounts of memory to be reserved, and does not require CS to contain the segment of the program segment prefix.
[3.0+] If the program is running on a network, it should remove all locks it has placed on file regions before terminating.
Example:
Terminate and stay resident, reserving enough memory to contain the entire program.
.
.
.
mov dx,offset pend ; DX = bytes to reserve
int 27h ; terminate, stay resident
.
.
.
pend equ $ ; offset, end of program
end