System information

FUNCTION 14: SELECT DISK

Entry Parameters:

The Select Disk function designates the disk drive named in register E as the default disk for

subsequent file operations, with E = 0 for drive A, 1 for drive B, and so on through 15,

corresponding to drive P in a full 16 drive system. The drive is placed in an on-line status, which

activates its directory until the next cold start, warm start, or disk system reset operation. If the

disk medium is changed while it is on-line, the drive automatically goes to a Read-Only status in

a standard CP/M environment, see Function 28. FCBs that specify drive code zero (dr = 00H)

automatically reference the currently selected default drive. Drive code values between I and 16

ignore the selected default drive and directly reference drives A through P.

FUNCTION 15: OPEN FILE

Entry Parameters:

Registers DE: FCB Address

Returned Value:

The Open File operation is used to activate a file that currently exists in the disk directory for the

currently active user number. The FDOS scans the referenced disk directory for a match in

positions 1 through 14 of the FCB referenced by DE (byte s1 is automatically zeroed) where an

ASCII question mark (3FH) matches any directory character in any of these positions. Normally,

no question marks are included, and bytes ex and s2 of the FCB are zero.

5.2 Call Conventions CP/M Operating System Manual

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