User`s guide

BDOS FUNCTION 49: GET / SET SYSTEM
CONTROLBLOCK
Entry Parameters:
Registers C: 31H
DE: SCB PB Address
Returned Value:
Registers A: Returned Byte
HL: Returned Word
Function 49 allows access to parameters located in the CP/M 3 System Control
Block (SCB). The SCB is a 100-byte data structure residing within the BDOS that
contains flags and data used by the BDOS, CCP and other system components. Note
that Function 49 is a CP/M 3 specific function. Programs intended for both MP/M 11
and CP/M 3 should either avoid the use of this function or isolate calls to this
function in CP/M 3 version-dependent sections.
To use Function 49, the calling program passes the address of a data structure
called the SCB parameter block in register pair DE. This data structure identifies the
byte or word of the SCB to be updated or returned. The SCB parameter block is
defined as:
SCBPB: DB OFFSET ; Offset within SCB
DB SET ; OFFH if settin!i a byte
; OFEH if setting a word
; 001H - OFDH are reserved
; OOOH if a get operation
DW VALUE ; Byte or word value to be set
The OFFSET parameter identifies the offset of the field within the SCB to be updated
or accessed. The SET parameter determines whether Function 49 is to set a byte or
word value in the SCB or if it is to return a byte from the SCB. The VALUE
parameter is used only in set calls. In addition, only the first byte of VALUE is
referenced in set byte calls.
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BDOS Function Calls CP/M 3 Programmers Guide