Note: This API call is for DOS and Win16 personality only. Use Family API for portability.

Int 28H

Version

2 and higher

Brief

DOS IDLE INTERRUPT

Family API

DosSleep

Input

SS:SP = top of MS-DOS stack for I/O functions

Return

all registers preserved

Macro

Notes

This interrupt is invoked each time one of the DOS character input
functions loops while waiting for input. Since a DOS call is in
progress even though DOS is actually idle during such input waits,
hooking this function is necessary to allow a TSR to perform DOS
calls while the foreground program is waiting for user input.	The
INT 28h handler may invoke any INT 21h function except functions
00h through 0Ch.

under DOS 2.x, the critical error flag (the byte immediately after the

InDOS flag) must be set in order to call DOS functions 50h/51h from
the INT 28h handler without destroying the DOS stacks.
calls to INT 21/AH=3Fh,40h from within an INT 28 handler may not use a
handle which refers to CON
at the time of the call, the InDOS flag (see INT 21/AH=34h) is normally
set to 01h; if larger, DOS is truly busy and should not be reentered
the default handler is an IRET instruction
supported in OS/2 compatibility box
the _MS-DOS_Programmer's_Reference_ for DOS 5.0 incorrectly documents
this interrupt as superseded
the performance of NetWare Lite servers (and probably other peer-to-
peer networks) can be dramatically improved by calling INT 28
frequently from an application's idle loop

See Also

INT 21/AH=34h,INT 2A/AH=84h,INT 2F/AX=1680h

Note

Text based on Ralf Brown Interrupt List Release 61

DOS API
Process manager	INT 20H, INT 21H: 00H, 25H, 26H, 31H, 34H, 35H, 4BH, 4CH, 4DH, 50H, 51H, 52H, 55H, 62H, INT 22H, INT 27H, INT 28H
File manager	INT 25H, INT 26H, INT 21H: 0DH, 0EH, 0FH, 10H, 11H, 12H, 13H, 14H, 15H, 16H, 17H, 19H, 1AH, 1BH, 1CH, 21H, 22H, 23H, 24H, 27H, 28H, 29H, 2EH, 2FH, 32H, 3305H, 36H, 39H, 3AH, 3BH, 3CH, 3DH, 3EH, 3FH, 40H, 41H, 42H, 4300H, 4301H, 45H, 45H, 46H, 4EH, 4FH, 54H, 56H, 5700H, 5701H, 5AH, 5BH, 5c00H, 5c01H, 60H, 67H, 68H, 6900H, 6901H, 6AH, 6CH
Character Device I/O	INT 29H, INT 21H: 01H, 02H, 03H, 04H, 05H, 06H, 07H, 08H, 09H, 0AH, 0BH, 0AH, 0CH, 5D07H, 5D08H, 5D09H, 5D0AH
Signals	INT 23H, INT 24H, INT 21H: 3300H, 3301H, 3302H
Memory manager	INT 21H: 48H, 49H, 4AH, 5800H, 5801H, 5802H, 5803H
Date and Time	INT 21H: 2AH, 2BH, 2CH, 2DH
Misc	INT 21H: 30H, 3306H, 3700H, 3701H, 3702H, 3703H, 59H
NLS	INT 21H: 3303H, 3304H, 3800H, 3801H, 6300H, 6301H, 6301H, 6500H, 6501H, 6502H, 6503H, 6504H, 6505H, 6506H, 6507H, 6520H, 6521H, 6522H, 6523H, 65A0H, 65A1H, 65A2H, 6601H, 6602H
Devices	INT 21H: 4400H, 4401H, 4402H, 4403H, 4404H, 4405H, 4406H, 4407H, 4408H, 4409H, 440AH, 440BH, 440CH, 440DH, 440EH, 440FH, 4410H, 4411H, 53H
Network	INT 21H: 5E00H, 5E01H, 5E02H, 5E03H, 5E04H, 5E05H, 5F00H, 5F01H, 5F02H, 5F03H, 5F04H, 5F05H, 5F07H, 5F08H
osFree Macro Library
Video I/O	@SetMode @SetCurSz @SetCurPos @GetCur @SetPage @ScrollUp @ScrollDn @Scroll @GetChAtr @PutChAtr @PutCh @SetPalet @SetColor @SetDot @GetDot @WrtTTY @VideoState @GetMode @GetDisplay @GetVideoState @GetEGAInfo @Cls
Hardware info	@Equipment @MemSize
Serial I/O	@AuxInit @AuxSendChar @AuxRecieveChar @AuxStatus
Tape I/O	@TapeOn @TapeOff @TapeRead @TapeWrite
Keyboard I/O	@KbdStatus @CharIn @CharPeek
Printer I/O	@PrnPrint @PrnInit @PrnStatus
Disk I/O	@DskReset @DskStatus @DskRead @DskWrite @DskVerify @DskFormat
Date and Time	@SetTime @GetTime
Mouse	@MouInit @MouShowPointer @MouStatus @MouSetPos @MouSetMickey @MouRegion
Memory manager	@ModBlok SET_BLOCK
Family API
DOS	Process Manager	DosBeep DosExit DosSleep DosExecPgm
File Manager	DosChDir DosChgFilePtr DosClose DosDelete DosDupHandle DosMkDir DosMove DosQCurDir DosQCurDisk DosSetFileMode DosOpen DosQFileInfo DosRead DosQFileMode DosQFSInfo DosQVerify DosRmDir DosSelectDisk DosFindClose DosFindFirst DosFindNext DosSetFileInfo DosSetVerify DosWrite DosFileLocks DosSetFHandState DosNewSize DosBufReset DosQFHandState DosSetFSinfo DosShutdown
Memory Manager	DosFreeSeg DosSubAlloc DosSubFree DosSubSet DosAllocHuge DosAllocSeg DosReallocHuge DosReallocSeg DosGetHugeShift DosCreateCSAlias
NLS	DosCaseMap DosGetCtryInfo DosGetDBCSEv DosSetCtryCode DosGetCollate DosGetMessage DosInsMessage DosPutMessage
Date and Time	DosSetDateTime DosGetDateTime
Devices	DosDevConfig DosDevIOCtl DosDevIOCtl2
Signals	DosHoldSignal DosSetSigHandler
Misc	BadDynLink DosGetEnv DosGetMachineMode DosGetVersion DosError DosErrClass DosSetVec
KBD	KbdCharIn KbdFlushBuffer KbdGetStatus KbdSetStatus KbdStringIn KbdPeek
VIO	VioGetBuf VioGetConfig VioGetCurPos VioGetCurType VioGetPhysBuf VioReadCellStr VioReadCharStr VioScrollUp VioScrollDn VioScrollLf VioScrollRt VioScrUnLock VioSetCurPos VioSetCurType VioSetMode VioGetMode VioShowBuf VioWrtCellStr VioWrtCharStr VioWrtCharStrAtt VioWrtNAttr VioWrtNCell VioWrtNChar VioWrtTTY VioScrLock VioPopUp
Tools	BIND
Modules	DOSCALLS.DLL VIOCALLS.DLL KBDCALLS.DLL MSG.DLL
Libraries	API.LIB OS2386.LIB FAPI.LIB DOSCALLS.LIB SUBCALLS.LIB