|DD_ASK_1||017B||Check to see if unit 1 is present|
Check to see if unit 1 is present. BASIC holds this information in bit 5 of the FLAGS3 system variable.
Turn motor on.
Fetch drive status.
If unit 1 is not-ready and write-protected, then unit 1 is missing. Start motor off timeout.
Note that this routine can be fooled by disks which are almost, but not quite, inserted in the drive.
This routine assumes that when a disk is not in the drive, then write-protect is true. This is indeed the case for 3 inch and 8 inch disk drives, but is not the case for 5 1/4 inch disk drives.
- If unit 1 present:
- Carry true
- Carry false
- A BC DE HL IX corrupt, all other registers preserved.