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| A: Interrupt Summaries |  |
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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)
0E 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 number 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)
MS-DOS 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)
MS-DOS 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 MS-DOS print spooler (Dummy-returns)
30 48 00C0 0000:0000 INT 48h-63h 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 F0D0:19E5 Host OSWRCH
4A 74 0128 F000:1E6D 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/PC-DOS 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 MS-DOS 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 MS-DOS 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 MS-DOS Reserved function ‡
1E 30 MS-DOS Reserved function ‡
1F 31 MS-DOS Reserved function ‡
20 32 MS-DOS 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
4B 75 Execute program
4C 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 MS-DOS Reserved function ‡
52 82 MS-DOS Reserved function ‡
53 83 MS-DOS Reserved function ‡
54 84 Get verify flag (non-functional in DOS Plus) ‡
55 85 MS-DOS 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 MS-DOS 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 MS-DOS Reserved function ‡
61 97 MS-DOS Reserved function ‡
62 98 Get PSP address (DOS Version 3.0+)‡
63 99 Get lead byte table (DOS Version 2.25 only) ‡
64 100 MS-DOS 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
1B 27 Get default drive data
1C 28 Get drive data
2E 46 Set verify flag
32 50 Get disc information (undocumented call) §
36 54 Get drive allocation data
54 84 Get verify flag
Directory Operations
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 byte (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 MS-DOS 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/O control (limited implementation)
E0 224 Call BDOS (see below)
INT E0h (BDOS) Summary by Function Number
In external (ie DOS resident console-connected) programs all functions are initiated by a call to INT 21h with a function 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
1B 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 MS-DOS or PC-DOS 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 Operations
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
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
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 10h to 14h are
14 20 reserved
15 21 Device initialisation
16 22 Check console output status
17 23 Calls 17h 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) <But see here - YP>
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
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