A: Interrupt Summaries

The Interrupt Vectors

It should be noted that these vectors are as set in an unexpanded 512 running an unmodified DOS Plus 2.1 with no software loaded except COMMAND.COM. Users are warned that loading almost any application program may damage some of the vectors. These vector contents should never be accessed directly.

Access should be either by an implicit program jump as a result of a call to the appropriate interrupt, or, when intercepting vectors, by the legal means of INT 21h function 25h or 35h.

In the table below the interrupts are grouped. In all cases the table shows the hex and decimal interrupt number, the offset of the vector in segment zero, the segment and offset of the vector contents and the function.

Internal	Hardware Interrupts
Interrupt	Seg0.			Vectored to
Hex	Dec	Offs	Seg:Offset	Function
00	 0	0000	06BB:47B5	Divide by zero overflow
0l	 1	0004	06BB:47CC	Single step error
02	 2	0008	06BB:119F	Non Maskable Interrupt 
03	 3	000C	06BB:47D6	Breakpoint
04	 4	0010	06BB:47DB	Overflow error
05	 5	0014	06BB:47E0	Bounds (range) error
06	 6	0018	06BB:47E5	Invalid Opcode
07	 7	001C	06BB:47EA	'ESC' opcode exception
08	 8	0020	06BB:1658	Hardware timer tick 
09	 9	0024	0000:0000	Not supported
0A	10	0028	0000:0000	Not supported
0B	11	002C	0000:0000	Not supported
0C	12	0030	06BB:0713	Tube register 1 or 4 interrupt 
0D	13	0034	0000:0000	Not supported
External Hardware Interrupts (IBM ROS Emulation)
0F	14	0038	0000:0000	Not supported (PC FDC)
0F	15	003C	0000:0000	Not supported (PC FDC)
10	16	0040	06BB:21F1	Display services for PC monitors 
11	17	0044	06BB:2729	Return equipment flags for PC 
12	18	0048	06B3:2734	Return memory size for PC 
13	19	004C	0B4E:06EE	if AH = 8 Return no. of floppy drives 
					else
					error = 'Unsupported IBM XT ROS call'
14	20	0050	06BB:2740	Async services int for PC Comm ports 
15	21	0054	068B:2801	Cassette services interrupt - Not supported
16	22	0058	06BB:2802	Keyboard Driver (Dummy - returns) 
17	23	005C	06BB.287A	Printer driver
18	24	0060	063B:2935	(ROM BASIC) 
19	25	0064	06BB:28EA	(Bootstrap loader) 
1A	26	0068	06BB:1661	IBM time of day
1B	27	006C	0B4E:10DC	IBM ROS kbd. break (Dummy-returns)$
1C	28	0070	06BB:4794	IBM ROS tick (Dummy - returns)
1D	29	0074	068B:2199	Video parameter address pointer 
1E	30	0078	06BB:218E	Disc parameter table pointer 
1F	31	007C	0000:0000	Not supported (Graphics char table in PC)
MSDOS Interrupts
20	32	0080	0B4E:0756	Terminate process (obsolete)
21	33	0084	0B4E:07B1	General function despatcher
22	34	0088	0B4E:069F	Terminate handler address 
23	35	008C	0B4E:08E1	CTRL-C handler address 
24	36	0090	0B4E:0A84	Critical error handler address 
25	37	0094	0B4E:0B43	Absolute disc read
26	38	0098	0B4E:0B99	Absolute disc write
27	39	009C	0B4E:0BBD	Terminate and stay resident (obsolete)
MSDOS Interrupts - Reserved for Future Use
28	40	00A0	06BB:4794	Wait for keyboard input (Dummy-returns)
29	41	00A4	0000:0000	INT 29h through to 2Eh are
2E	46	00B8	O000:0000	not supported - vectors zero
2F	47	00BC	06BB:4794	MSDOS print spooler (Dummy - returns)
30	48	00C0	0000:0000	INT 48h 43h are
3F	63	00FC	0000:0000	not supported - vectors zero
40	64	0100	F000:lDAC	Host OSFIND (f/disc driver on PC/XT)
41	65	0104	F000:1DCF	Host OSGBPB (h/disc param. table PC/XT)
42	66	0108	F00D:1F1F	Host OSBPUT
43	67	Ol0C	F000:1F3B	Host OSBGET
44	68	0110	F000:1F4F	Host OSARGS (Graphics chr. table PC Jnr)
45	69	0114	F000:1F93	Host OSFILE
46	70	0118	F000:19B0	Host OSRDCH
47	71	011C	F000:19D8	Host OSASCI
48	72	0120	F000:19DD	Host OSNEWL
49	73	0124	FODO:19E5	Host OSWRCH
4A	74	0128	FO00:1E6D	Host OSWORD
4B	75	012E	F000:1E10	Host OSBYW
4C	76	0130	F000:lA11	Host OSCLI
4D	77	0134	0000:0000	Not supported
4E	78	0138	0000:0000	Not supported
4F	79	013C	F000:2048	80186 error handler
50	80	0140	0000:0000	INTs 50h to DFh are
DF	223	037C	0000:0000	not supported - vectors zero
In the above range 60h to 67h are the user vectors, while 67h is used for EMS in later PCs.
CP/M (86)/BDOS calls (Available to DOS Plus)
E0	224	0380	0060:0144	Direct call to BDOS (See below)
					Unused - Reserved for Future MS/PCDOS Expansion
El	225	0384	0000:0000	INTs Elh to FDh are
F0	253	03F4	0000:0000	not supported - vectors zero
Acorn 512 'Specials'
FE	254	03F8	06BB:4795	SYSDAT vector for GEM (Kills INT 224)
FF	255	03FC	06BB:47F4	80186 register dump on critical error
	These are pointers to code or data tables and must not be called directly.
	These are incomplete implementations or supply suitable simulated return information.

INT 21h Summary by Function Number

In the following list all interrupt functions are shown for completeness. The function number is always in register AH.

A '' indicates that the function is available in MSDOS v2.0 onwards, but is not officially recognised or supported by the Microsoft Corporation.

A against the function indicates that the call is incompatible with DOS Plus 2.1 for the reason shown.

Hex Dec Function type
00  00  Terminate process
01  01  Character input with echo
02  02  Character output
03  03  Auxiliary input
04  04  Auxiliary output
05  05  Printer output
06  06  Direct console input/output
07  07  Unaltered character input no echo
08  08  Character input without echo
09  09  Display string
0A  10  Buffered keyboard input
0B  11  Check input status
0C  12  Flush input buffer then input
0D  13  Drive reset
0E  14  Select drive
0F  15  Open file
10  16  Close file
11  17  Find first file
12  18  Find next file
13  19  Delete file
14  20  Sequential read
15  21  Sequential write
16  22  Create file
17  23  Rename file
18  24  MSDOS Reserved function 
19  25  Get current drive
1A  26  Set disc transfer area (DTA) address
1B  27  Get default drive data
1C  28  Get drive data
1D  29  MSDOS Reserved function 
1E  30  MSDOS Reserved function 
1F  31  MSDOS Reserved function 
20  32  MSDOS Reserved function 
21  33  Random read
22  34  Random write
23  35  Get file size
24  36  Set relative record number
25  37  Set interrupt vector
26  38  Create new PSP
27  39  Random block read
28  40  Random block write
29  41  Parse filename
2A  42  Get date
2B  43  Set date
2C  44  Get time
2D  45  Set time
2E  46  Set verify flag (non-functional in DOS Plus)
2F  47  Get DTA address
30  48  Get DOS version number
31  49  Terminate and stay resident
32  50  Get disc information (undocumented call) 
33  51  Get or set break flag (non-functional in DOS Plus)
34  52  Find active byte (undocumented call) 
35  53  Get interrupt vector
36  54  Get drive allocation data
37  55  Set or get DOS switch character
38  56  Get or set country information
39  57  Create directory
3A  58  Delete directory
3B  59  Set current directory
3C  60  Create file
3D  61  Open file
3E  62  Close file
3F  63  Read file or device
40  64  Write file or device
41  65  Delete file
42  66  Set file pointer
43  67  Get or set file attributes
44  68  I/O control
45  69  Duplicate handle
46  70  Redirect handle
47  71  Get current directory
48  72  Allocate memory block
49  73  Release memory block
4A  74  Resize memory block
45  75  Execute program
46  76  Terminate process with return code
4D  77  Get return code
4E  78  Find first file
4F  79  Find next file
50  80  Set address of PSP (undocumented call) 
51  81  MSDOS Reserved function 
52  82  MSDOS Reserved function 
53  83  MSDOS Reserved function 
54  84  Get verify flag (non-functional in DOS Plus) 
55  85  MSDOS Reserved function 
56  86  Rename file (not implemented) 
57  87  Get or set file date and time stamps (not implemented) 
58  88  Get or Set allocation strategy (DOS Version 3.0+) 
59  89  Get extended error information (DOS Version 3.0+) 
5A  90  Create temporary file (DOS Version 3.0+) 
5B  91  Create new file (DOS Version 3-0+) 
5C  92  Lock or unlock file region (DOS Version 3.0+) 
5D  93  MSDOS Reserved function 
5E  94  Get machine name/Get or set printer setup (DOS Version 3.1+) 
5F  95  Device redirection (DOS Version 3.1+) 
60  96  MSDOS Reserved function 
61  97  MSDOS Reserved function 
62  98  Get PSP address (DOS Version 3.0+) 
63  99  Get lead byte table (DOS Version 2.25 only) 
64  100 MSDOS Reserved function 
65  101 Get extended country information (DOS Version 3.3+) 
66  102 Get or set code page (DOS Version 3.3+) 
67  103 Set handle count (DOS Version 3.3+) 
68  104 Commit file (DOS Version 3.3+) 
E0  224 Call BDOS (See below)

INT 21h Function Summary by Operation Type

In the following list only interrupts compatible with DOS version 2 and which should be available in DOS Plus 2.1 are shown. where a function has (v.1) shown, it is the original implementation from DOS version 1 and has been superseded or has improved facilities in the later call referred to, which should generally be used in preference. Calls marked are not usable in the 512 even though they are DOS 2.1 calls.

Hex Dec Function type
Character Input/output
0l  1 Character input with echo
02  2 character output
03  3 Auxiliary input
04  4 Auxiliary output
05  5 Printer output
06  6 Direct console input/output
07  7 Unfiltered character input without echo
08  8 Character input without echo
09  9 Display string
0A 10 Buffered keyboard input
0B 11 Check input status
0C 12 Flush input buffer then input
Disc Operations
0D 13 Drive reset
0E 14 Select drive
19 25 Get current drive
18 27 Get default drive data
1C 28 Get drive data
   46 Set verify flag
32 50 Get disc information (undocumented call) 
36 54 Get drive allocation data
54 84 Get verify flag
Directory Functions
39 57 Create directory
3A 58 Delete directory
3B 59 Set current directory
47 71 Get current directory
File operations
0F 15 Open file (V.1 use 3D)
10 16 Close file (V.1 use 3E)
11 17 Find first file(V.1 use 4E)
12 18 Find next file (V.1 use 4F)
13 19 Delete file (V.1 use 41)
16 22 Create file (V.1 use 3C)
17 23 Rename file
23 35 Get file size
29 41 Parse file name
3C 60 Create file
3D 61 Open file
3E 62 Close file
41 65 Delete file
43 67 Get or set file attributes
45 69 Duplicate handle
46 70 Redirect handle
4E 78 Find first file
4F 79 Find next file
56 86 Rename file
57 87 Get or set file date and time
Record Operations
14 20 Sequential read
15 21 Sequential write
lA 26 Set disk transfer area (DTA) address
21 33 Random read (See 27)
22 34 Random write (See 28)
24 36 Set relative record number
27 39 Random block read
28 40 Random block write
2F 47 Get DTA address
3F 63 Read file or device
40 64 Write file or device
42 66 set file pointer
Process Management
00 00 Terminate process (V.1 use 4C)
26 38 Create new PSP (V.1 use 4B)
31 49 Terminate and stay resident
34 52 Find active byle (undocumented call) 
4B 75 Execute program
4C 76 Terminate process with return code
4D 77 Get return code
50 80 Set address of PSP (undocumented call) 
Memory Management
48 72 Allocate memory block
49 73 Release memory block
4A 74 Resize memory block
Time/Date Functions
2A 42 Get date
2B 43 Set date
2C 44 Get time
2D 45 Set time
Miscellaneous System Functions
25  37 Set interrupt vector
30  48 Get MSDOS version number
33  51 Get or set break flag: (not implemented) 
35  53 Get interrupt vector
37  55 Set or get DOS switch character
38  56 Get or set country information
44  68 I/0 control (limited implementation)
E0 224 Call BDOS (see below)

INT E0h (BDOS) Summary by Function Number

In external (i.e. DOS resident console-connected) programs, all functions are initiated by a call to INT 21h with a fundion code of 0E0h in AH and the BDOS function number in CL. There are gaps in the sequence, either because the call is not implemented up to 2.1, or because it is a pure CP/M function not available in DOS Plus.

Hex Dec Function type
00  0 Terminate program (exactly as 8Fh)
01  1 Read a character
02  2 Write a character
03  3 Auxiliary input
04  4 Auxiliary output
05  5 Write a character to the list device
06  6 Direct console I/O
07  7 Auxiliary input status
08  8 Auxiliary output status
09  9 String output
0A 10 Read an edited line
0B 11 Get console status
0C 12 Get BDOS version number
0D 13 Reset all drives
0E 14 Set default drive
0F 15 Open a file for record access
10 16 Close a file
11 17 Search for first matching file
12 18 Search for next matching file
13 19 Delete a file
14 20 Read records sequentially
15 21 Write records sequentially
16 22 Create a file entry
17 23 Rename a file
18 24 Return 'Login Vector' for all logged in drives
19 25 Return the default drive ID
1A 26 Set the DMA buffer offset address
18 27 Get address of disc allocation vectors
1C 28 Set the default drive to read-only
1D 29 Get read-only drive vectors
lE 30 Set file attributes
1F 31 Get calling process's default disc DPB address
20 32 Get/set current user number
21 33 Read random records
22 34 Write random records
23 35 Return the size of a file
24 36 Set the random record number in the FCB
25 37 Reset the specified drives
26 38 Unallocated
27 39 Free specified drives
28 40 Write random records and zero-fill unallocated blocks
29 41 Unallocated
2A 42 Unallocated
2B 43 Unallocated
2C 44 Set the system multi-sector count
2D 45 Set filing system error mode
2E 46 Return unallocated space on the specified drive
2F 47 Load and execute program specified in DMA buffer
30 48 Write pending internal disc buffers to media
31 49 Get/set system variable
32 50 Call BIOS (XIOS) directly (See below)
33 51 Set the DMA buffer segment address
34 52 Return segment:offset of DMA buffer
35 53 Allocate maximum memory available in system
36 54 Allocate maximum memory available at specified address
37 55 Allocate a segment as specifed in MCB
38 56 Allocate specified memory at specified address
39 57 Free memory starting at a specified address
3A 58 Unallocated
3B 59 Load CMD file into memory
3C 60 Call RSX program
3D 61 Calls 3Dh to 62h are
62 98 unallocated
63 99  Truncate file to the specified random record number
64 100 Create or update a directory label
65 101 Get directory label data byte for specified drive
66 102 Return a file's date/time stamps and password mode
67 103 Create or update a file's extended FCB
68 104 Set internal date and time
69 105 Get internal date and time
6A 106 Set the default password
6B 107 Get the DOS Plus serial number (Not version number)
6C 108 Get/set program return cole
6D 109 Get/set console mode
6E 110 Get/set output delimiter
6F 111 Write a specified block of characters
70 112 Write a specified number of characters to the list device
71 113 Calls 71h to 8Ch are
8C 140 unallocated
8D 141 Delay a specified number of ticks (wait)
8E 142 Relinquish processor to other programs (multitasking)
8F 143 Terminate program (exactly as 0)
90 144 Calls 90h to 92h are
92 146 unallocated
93 147 Detach program from console (enter background)
94 148 Calls 94h to 97h are
97 151 Unallocated
98 152 Parse ASCII string and initialise FCB
99 153 Unallocated
9A 154 Get System data area (SYSDAT) address
95 155 Calls 95h to ADh are
AB 171 Unallocated
AC 172 Read characters from AUXIN
AD 173 Send characters to AUXOUT
AE 174 Calls AEh to FF are
FF 255 unallocated

INT E0h Function Summary by Operation Type

The BDOS call summary shown below groups functions by operation type. The list is essentially in numerical order within operations, but where two functions complement each other they have been placed together if this does not occur naturally.

It must be remembered that, in CP/M disc formats a directory sub- structure is not supported, nor is file date/time stamping the norm (although this can be initiated by the DOS Plus INIT command). Many of the disc and file handling calls may, therefore, not be appropriate for use with MSDOS or PCDOS disc formats.

In CP/M, files are protected or separated from each other by being assigned to a group under different user numbers (0 to 15) rather than by being placed in different directories. In CP/M, media attributes can be set at disc and/or file level which can, even in direct BDOS calls, prevent or restrict unanthorised access to files in several different ways.

Hex	Dec	Function type
		Auxiliary character I/O
03	3	Auxiliary input
04	4	Auxiliary output
07	7		Auxiliary input status
08	8	Auxiliary output status
AC	172	Read characters from AUXIN
AD	173	Send characters to AUXOUT
Console Input/Output
01	1	Read a character
02	2	Write a character
06	6	Direct console I/O
09	9	String output
0A	10	Read an edited line
0B	11	Get console status
6D	109	Get/set console mode
6E	110	Get/set output delimiter
6F	111	Write a specified block of characters
93	147	Detach program from console (enter background)
Disc Drive open functions
0D 13 Reset all drives
0E 14 Set default drive
18 24 Return 'Login Vector' for all logged in drives
19 25 Return the default drive ID
1B 27 Get address of disc allocation vectors
1C 28 Set the default drive to read-only
10 29 Get read-only drive vectors
1F 31 Get calling process's default disc DPB address
25 37 Reset the specified drives
27 39 Free specified drives
2E 46 Return unallocated space on the specified drive
30 48 Flush (write) pending internal disc buffers to media
64 100 Create or update a directory label
65 101 Get directory label data byte for specified drive
File Operations
0F 15 Open a file for record access
10 16 Close a file
11 17 Search for first matching file
12 Is Search for next matching file
13 19 Delete a file
14 20 Read records sequentially
15 21 Write records sequentially
16 22 Create a file entry
17 23 Rename a file
1A 26 Set the DMA buffer offset address
1E 30 set file attributes
20 32 Get/set current user number
21 33 Read records randomly
22 34 Write records randomly
23 35 Return the size of a file
24 36 set the random record number in the PCB
28 40 Write random records and zero-fill unallocated blocks
2C 44 Set the system multi-sector count
2D 45 Set filing system error mode
33 51 Set the DMA bufkr segment address
34 52 Return segment:offset of DMA buffer
63 99 Truncate file to the specified random record number
66 102 Return a file's date/time stamps and password mode
67 103 Create or update a files extended FCB
6A 106 Set the default password
98 152 Parse ASCII string and initialise FCB
List Device Calls
05   5 Write a character to the list device
70 112 Write a specified number of characters to the list device
Process Management
00 0	Terminate program (exactly as 8Fh)
2F 47	Load and execute program specified DMA buffer
3B 59	Load CMD file into memory
3C 60	Call RSX program
6C 108	Get/set program return code
8D 141	Delay a specified number of ticks (wait)
8E 142	Relinquish processor to other programs (multitask)
8F 143	Terminate program (exactly as 00)
Memory Management
35 53 Allocate maximum memory available in system
36 54 Allocate maximum memory available at specified address
37 55 Allocate a segment as specified in MCB
38 56 Allocate specified memory at specified address
39 57 Free memory starting from a specified address
Time/Date Functions
68 104 Set internal date and time
69 105 Get internal date and time
	(NB: Time is in hours and minutes only) 
Miscellaneous Functions
0C  12 Get BDOS version number
31  49 Get/set system variable
32  50 Call BIOS (XIOS) directly (See below)
6B 107 Get the DOS Plus serial number (Not version number)
9A 154 Get Sytem data area (SYSDAT) address

INT E0h Function 32h XIOS Subfunctions

Within interrupt E0h is function 32h, which gives another range of subfunctions, direct calls to the XIOS. As usual CL is set to the interrupt function number, are, while DS:DX are used as pointers to the memory location containing the XIOS call parameters

As can be seen, many of the standard CP/M functions are almost identical to the slightly easier to use BDOS functions and hence are of little advantage. The block of functions with values of 80h or greater are peculiar to the XIOS as implemented for Acorn 6502 host systems, while function 80h itself is provided for use within the BDOS and the bootstrap loader.

Hex Dec Function type
00  00  Terminate program (Same as BDOS function 0/8Fh)
0l  01  As above
02  02  Check for console input status
03  03  Read character from console
04  04  Write character to console
05  05  Write character to list device
06  06  Write character to auxiliary device
07  07  Read character from auxiliary device
0F  15  Return list device status
10 16 Calls l0h to l4h are
14 20 reserved
15 21 Device initialisation
16 22 Check console output status
17  23 Calls l7h to 7Fh are
7F 127 reserved
80 128 XIOS version (ACORN specific)
81 129 Get tube semaphore
82 130 Release the semaphore
83 131 Select text-graphics
84 132 Update graphics rectangle (B&W)
85 133 Update graphics rectangle (colour)
86 134 Get release/update mouse
87 135 Get system error info
88 136 Entry in CLOCK called by WatchDog RSP
89 137 BBC OSBYTE function
8A 138 BBC OSWORD function