User`s guide

BDOS FUNCTION 60: CALL RESIDENT SYSTEM
EXTENSION
Entry Parameters:
Registers C: 3CH
DE: RSX PB Address
Returned Value:
Registers A: Error Code
H: Physical Error
Function 60 is a special BDOS function that you use when you call Resident
System Extensions. The RSX subfunction is specified in a structure called the RSX
Parameter Block, defined as follows:
RSXPB: db FUNC ; RSX Function number
db NUMPARMS ; Number of word Parameters
dw PARMETER1 ; Parameter I
dw PARMETER2 ; Parameter 2
. . .
dw PARMETERN ; Parameter n
RSX modules filter all BDOS calls and capture RSX function calls that they can
handle. If there is no RSX module present in memory that can handle a specific RSX
function call, the call is not trapped, and the BDOS returns OFFH in registers A and
L. RSX function numbers from 0 to 127 are available for CP/M 3 compatible soft-
ware use. RSX function numbers 128 to 255 are reserved for system use.
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BDOS Function Calls CP/M 3 Programmers Guide