CP/M 3, MP/M II and CP/Net hardware error codes

Normally, if a hardware (or similar) error is encountered CP/M will print a message describing the error and then quit to the command prompt. In CP/M 3, BDOS function 45 can be used to modify this behaviour, so that error codes are returned to the program instead.

The codes returned are in the H register:

 0 - Software error (eg file not found)
 1 - Select error (cannot access drive)
 2 - Disc is read-only
 3 - File is read-only
 4 - Invalid drive
 5 - File already open
 6 - FCB checksum error (MP/M II) - the calling program has tampered with the FCB.
 7 - Password error
 8 - File already exists
 9 - Filename contains ?
10 - Wheel protection error (ZPM3) / Too many files open (MP/M II)
11 - No room in system lock list (MP/M II)
12 - Not logged on to server (CP/Net)

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