Function 51h "Used Internally by DOS" - Get Program Segment Prefix* Returns the PSP address of currently executing program
entry AH 51h
return BX address of currently executing program
offset
00h program exit point
02h memory size in paragraphs
04h unused (0)
05h CP/M style entry point (far call to DOS)
0Ah terminate address (old int 22h)
0Ch terminate segment
0Eh break address (old int 23h)
10h break segment
12h error address (old int 24h)
14h error segment
16h parent PSP segment
18h DOS 2.0+ open files, 0FFh = unused
2Ch DOS 2.0+ environment segment
2Eh far ptr to process's SS:SP
32h DOS 3.x max open files
34h DOS 3.x openfile table address
36h DOS 3.x openfile table segment
38h unused by DOS versions struct#fcb">= 3.3
50h DOS function dispatcher (FAR routine)
53h unused
55h Struct -FCB #1 extension
5Ch Struct -FCB #1
6Ch Struct -FCB #2
80h command tail / default DTA buffer
note 1) Used in DOS 2.x, 3.x uses 62h
2) Function 51h is dangerous in background operations prior to DOS 3.x as
it uses the wrong stack for saving registers. (same as functions
0..0Ch in DOS 2.x)
3) 50h and 51h might be used if you have more than one process in a PC.
For instance if you have a resident program that needs to open a file
you could first call 51h to save the current id and then call 50h to set
the ID to your PSP.
4) Under DOS 2.x, this function cannot be invoked inside an int 28h handler
without setting the Critical Error flag
5) Used by DOS 3.3 PRINT, DEBUG
file: /Techref/INT/21f/51.htm, 2KB, , updated: 1999/4/26 12:31, local time: 2024/8/31 18:31,
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