User`s guide

BDOS FUNCTION 50: DIRECT BIOS CALLS
Entry Parameters:
Registers C: 32H
DE: BIOS PB Address
Returned Value: BIOS RETURN
Function 50 provides a direct BIOS call through the BDOS to the BIOS. The
calling program passes the address of a data structure called the BIOS Parameter
Block (BIOSPB) in register pair DE. The BIOSPB contains the BIOS function number
and register contents as shown below:
BIOSPB: db FUNC ; BIOS function no.
db AREG ; A register contents
dw BCREG ; BC register contents
dw DEREG ; DE register contents
dw HLREG ; HL register contents
System Reset (Function 0) is equivalent to Function 50 with a BIOS function
number of 1.
Note that the register pair BIOSPB fields (BCREG, DEREG, HLREG) arc defined
in low byte, high byte order. For example, in the BCREG field, the first byte contains
the C register value, the second byte contains the B register value.
Under CP/M 3, direct BIOS calls via the BIOS jump vector are only supported for
the BIOS Console I/O and List functions. You must use Function 50 to call any other
BIOS functions. In addition, Function 50 intercepts BIOS Function 27 (Select Mem-
ory) calls and returns with register A set to zero. Refer to the CPIM Plus (CP/M
Version 3) Operating System System Guide for the definition of the BIOS functions
and their register passing and return conventions.
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BDOS Function Calls CP/M 3 Programmers Guide