5.4 BDOS Function Calls
BDOS includes many utility subroutines which input or output data
to
and from
peripherals and handle files. These subroutines are referred to as BDOS func-
tions, and can easily be used in your own programs as shown below. There are
39 BDOS functions which can be utilised; any
of
these can be used by calling
address 0005H with a function number in register C and a parameter in register
pair DE. Single byte values will be returned in register A while double byte values
are returned in register pair HL.
The BDOS functions are listed below. In this list, the entry parameters are those
which are passed
to
BDOS from the user program which calls the function,
and the return parameters are those which are passed
to
the user program from
the function called.
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Table 5 2
Function No.
0:
1
2
3
4
5
6
7
8
9
10
I
11
12
13
14
--
Explanation
Entry Parameter
This function returns control to C
OOH
the CPIM
command
level.
This function reads a character
C:
01H
from
CON
This function outputs a charac-
C:
02H
ter to CON:
E:
Character to
be
output
This function reads a character
C:
03H
from
RDR:
This function outputs a charac·
C:
04H
ter to PUN:
E:
Character to
be
output
This function outputs a charac-
C
05H
ter to LST:
E:
Character to
be
output
This
function proVides direct
C:
06H
console input and
output
opera-
E
For
input,
tion. It bypasses
all
CPIM nor-
OFFH
mal control character functions For output, the
such
as
"CTRL"
+
"P.".
character to
be
output.
This function returns the current
C:
07H
contents of IOBYTE.
This function sets a
new
value
in
C:
08H
IOBYTE.
E:
Value
to
be
set in IOBYTE
This
function
outputs
the
C:
09H
character string starting at the
DE:
Starting ad-
specified
address and ending
dress
of
the
with
"$"
to CON:
memory area in
which
the cha-
racter
string
is
stored
This function reads a character
C
OAH
string from
CON:
into the buf-
DE:
Starting ad-
fer area starting at the specified
dress
C)f
the buf-
address. fer area
This function reads the status of
C:
OBH
CON:
This function returns the version
C:
OCH
number
of the CP/M system
currently
in
use.
This function
sets all disks to C
ODH
read/write, selects drive A and
sets the default DMA address to
0080H.
This
function
selects
the
C:
OEH
specified disk drive.
E:
Name of drive
to
be
selected
5-5
Returned value
A:
Read
character
A:
Read
character
I
A:
For input, the character
read
OOH
is
returned when
CON:
is
not ready.
A:
Contents of IOBYTE
Buffer: Character string read
from
CON:
A:
CON:
status FFH -
CON:
ready
OOH
-
CON:
not ready
H:
CPIM or MP/M
L:
Version number
(Continued)
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