PC Hardware in a Nutshell, 3rd Edition

Using Cable Select

All recent ATA/ATAPI drives provide a Cable Select (CS or CSEL) jumper in addition to the standard Master/Slave jumpers. If you jumper a drive as Master (or Slave), that drive functions as Master (or Slave) regardless of which connector it is attached to on the ATA cable. If you jumper a drive as CSEL, the position of the drive on the cable determines whether the drive functions as a Master or a Slave.

CSEL was introduced in the ATA-2 and ATA-3 specifications as a means to simplify ATA configuration. The goal was that eventually all ATA/ATAPI devices would be configured to use CSEL. That would mean that drives could simply be installed and removed without changing jumpers, with no possibility of conflict due to improper jumper settings. Although CSEL has been around for years, it has only recently become popular with system makers. If you work on a PC built in the last year or two, you may encounter CSEL, so it’s good to be aware of it.

Using CSEL requires the following:

• If one drive is installed on the interface, that drive must support and be configured to use CSEL. If two drives are installed, both must support and be configured to use CSEL.

• The ATA interface must support CSEL. For this to be true, the ATA interface must ground Pin 28. On many older ATA interfaces, Pin 28 is open or high, and so cannot be used for CSEL. If Pin 28 is not grounded on the interface, any drive configured as CSEL that connects to that interface is configured as Slave.

• The ATA cable ...