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Home CPM 80 CPM BDOS BDOS System Services

BDOS System Services


The System Services provide a program with the ability to terminate and resart CPM as well as check the version of the CPM operating system.

Function 0: System Reset
Entry C 00H
Return (none)

The System Reset function returns control to the CP/M operating system at the CCP level. The CCP reinitializes the disk subsystem by selecting and logging-in disk drive A. This function has exactly the same effect as a jump to location BOOT.


Function 12: Return Version Number
Entry C 0CH
Return HL Version Number

Function 12 provides information that allows version independent programming. A two-byte value is returned, with H = 00 designating the CP/M release (H = 01 for MP/M) and L = 00 for all releases previous to 2.0. CP/M 2.0 returns a hexadecimal 20 in register L, with subsequent version 2 releases in the hexadecimal range 21, 22, through 2F. Using Function 12, for example, the user can write application programs that provide both sequential and random access functions.

Last Updated on Wednesday, 25 March 2009 14:25