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BDOS.HLP
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2000-06-30
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BDOS - Basic I/O Operations/Functions
BDOS - Basic Disk Operations/Functions
Console Read Buffer Organization/Meaning (re: BDOS Function 10)
File Control Block Organization/Meaning
:BDOS - Basic I/O Operations
Function and Number Input Parameters Output Parameters
System Reset 0 None None
Read Console 1 None ASCII Char in A
Write Console 2 ASCII Char in E None
Read Reader 3 None ASCII Char in A
Write Punch 4 ASCII Char in E None
Write List 5 ASCII Char in E None
Direct Con I/O 6 ASCII Char in E I/O Status in A if E=0FFH
*All function numbers are passed in Reg C.
~
Function and Number Input Parameters Output Parameters
Get I/O Status 7 None I/O Status in A
Put I/O Status 8 I/O Status in E None
Print Buffer 9 Address of string None
terminated by $
in DE
Read Buffer 10 Address of Read Read Buffer is filled
Buffer in DE (See Section on Organization)
Console Ready 11 None LSB of A is 1 if char
ready
Return Version # 12 None Version Info in HL
H=0 CP/M, H=1 MP/M
L=00 CP/M 1.x, 2x 2.x
*All function numbers are passed in Reg C.
:BDOS - Basic Disk Operations
Function and Number Input Parameters Output Parameters
Init BDOS 13 None None
Log-In Disk 14 Value in Reg E None
A=0, B=1, C=2,
D=3
Open File 15 Address of FCB Byte address of FCB
in DE if found or 0FFH if not
Close File 16 Address of FCB Byte address of FCB
in DE if found or 0FFH if not
Search for File 17 Address of FCB Byte address of FCB (0-3)
in DE if found or 0FFH if not
Search for Next 18 Address of FCB Byte address of next FCB
in DE if found or 0FFH if not
Delete File 19 Address of FCB Byte address of FCB (0-3)
in DE if found or 0FFH if not
*All function numbers are passed in Reg C.
~
Function and Number Input Parameters Output Parameters
Read Next Record 20 Address of FCB 0=successful readè in DE 1=read past EOF
2=reading random data
Write Next Rec 21 Address of FCB 0=successful write
in DE 1=error in extending
2=end of disk data
255=no more dir space
Make File 22 Address of FCB Byte address of FCB or
in DE 255 if no more dir space
Rename FCB 23 Address of FCB Byte Address of Dir entry
in DE or 255 if no match
Return Log Code 24 None Login vector in HL
Read Drive No 25 None Number of logged-in drive
(A=0, B=1, C=2, D=3)
Set DMA Address 26 Address of 128 None
byte buffer in DE
*All function numbers are passed in Reg C.
~
Function and Number Input Parameters Output Parameters
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HL
Write Prot Disk 28 None None
Get R/O Vect 29 None HL=R/O Vect Val
Set File Attrib 30 Ptr to FCB in DE Dir code in A
Get Disk Parms 31 None HL=DPB Address
Set/Get Usr Code 32 E=0FFH (get)/Code A=Current code (get)/no
(set) value (set)
*All function numbers are passed in Reg C.
NOTE: Functions 28-32 should be avoided in application programs in order to
maintain upward compatibility with CP/M.
~
Function and Number Input Parameters Output Parameters
Read Random 33 DE=FCB addr A=return code
1=reading unwritten data
2=(not used)
3=can't close curr ext
4=seek to unwritten ext
5=(not used)
6=seek past end of disk
Write Random 34 DE=FCB addr A=return code
1=reading unwritten data
2=(not used)
3=can't close curr ext
4=seek to unwritten ext
5=dir overflow
6=seek past end of disk
*All function numbers are passed in Reg C.
NOTE: Functions 28-32 should be avoided in application programs in order to
maintain upward compatibility with CP/M.
~
Function and Number Input Parameters Output Parameters
Compute File Siz 35 DE=FCB addr Random Rec Field set
to file size
Set Random Rec 36 DE=FCB addr Random Rec Field set
Reset Drive 37 DE=Drive Vector A=return code, Always 00h
Write Random 40 DE=FCB addr A=return code
(w/zero fill) 1=reading unwritten data
2=(not used)
3=can't close curr ext
4=seek to unwritten ext
5=dir overflow
6=seek past end of disk
*All function numbers are passed in Reg C
NOTE: Functions 28-32 should be avoided in application programs in order to
maintain upward compatibility with CP/M.
:Console Read Buffer Organization/Meaning (re: BDOS Function 10)
Refer to BDOS function 10 'Read Console Buffer'
Byte Function
1 Maximum Buffer Length (1 to 255)
2 Current Buffer Length (returned value)
No. of characters in the buffer
3-n Data (returned values)
The actual characters read from the console and in the buffer.
If the number of characters in the buffer is less than the length of the
buffer, then uninitialized positions follow the last character. Also note
that certain functions that return the carriage return to the leftmost
position (e.g., ctl-X), do so only to the column position where the prompt
ended.
:File Control Block Organization/Meaning
In file operations, starting with Function 15, Register DE usually
addresses a file control block. Transient programs often use the default
file control block at location BOOT+005Ch (normally 005Ch), for simple file
operations.
The basic unit of file information is a 128-byte record used for all
file operations; thus, a default location for disk I/O is provided by CP/M at
location BOOT+0080h (normally 0080h), which is the initial default DMA address
(see function 26). All directory operations take place in a reserved area that
does not effect write buffers, with the exception of Search First and Search
Next.
The FCB data area consists of a sequence of 33 bytes for sequential
access and a series of 36 bytes in the case when the file is accessed randomly.
The default FCB, normally located at 005Ch, can be used for random access
files, since the three bytes starting at BOOT+007Dh are available for this
purpose.
~
The FCB format is as follows:
dr f1 f2 / / f8 t1 t2 t3 ex s1 s2 rc d0 / / dn cr r0 r1 r2
00 01 02 ... 08 09 10 11 12 13 14 15 16 ... 31 32 33 34 35
where dr drive code (0-16)
0 use default drive for file
1 auto disk select drive A
2 auto disk select drive B
....
16 auto disk select drive P
f1...f8 contain the file name in ASCII upper case,
with high bit = 0
t1,t2,t3 contain the file type in ASCII upper case, with high
bit = 0 t1, t2 and t3 denote the bit of these positions
t1 Read Only file
t2 Systom File, not Directory listing
~
dr f1 f2 / / f8 t1 t2 t3 ex s1 s2 rc d0 / / dn cr r0 r1 r2
00 01 02 ... 08 09 10 11 12 13 14 15 16 ... 31 32 33 34 35
where ex contains the current extent number, normally set to 00
by the user, but in the range of 0-31 during file I/O
s1 reserved for internal system use
s2 reserved for internal system use, set to zero on call
to OPEN, MAKE, SEARCH
rc record count of extent 'ex'. value from 0-127.
d0...dn filled-in by CP/M, reserved for system use
cr current record to read or write in a sequential file
operation. normally set to zero by the user.
r0,r1,r2 optional random record number in the range 0-65535,
with overflow to r2,r0,r1 constitute a 16 bit value
with low byte r0, and high byte r1.