Hardware Reference
In-Depth Information
an unkeyed ATA drive to your computer, turn on the computer, and it seems as if the sys-
temislockedup(youdon'tseeanythingonthescreen),checktheATAcable.(See
Figure
7.6
for examples of unkeyed and keyed ATA cables.)
In rare situations in which you are mixing and matching items, you might encounter a
cable with pin 20 blocked (as it should be) and a board with pin 20 still present. In that
case, you can break off pin 20 from the board—or for the more squeamish, remove the
block from the cable or replace the cable with one without the blocked pin. Some cables
have the block permanently installed as part of the connector housing, in which case you
must break off pin 20 on the board or device end or use a different cable.
The simple rule of thumb is that pin 1 should be oriented toward the power connector on
the device, which normally corresponds to the stripe on the cable.
PATA I/O Cable
A 40-conductor ribbon cable is specified to carry signals between the bus adapter circuits
andthedrive(controller).Tomaximize signalintegrityandeliminate potential timingand
noiseproblems,thecableshouldnotbelongerthan18inches(0.46meters),althoughtest-
ing shows that you can reliably use 80-conductor cables up to 27 inches (0.69 meters) in
length.
Note that ATA drives supporting the higher-speed transfer modes, such as PIO Mode 4
or any of the Ultra-DMA (UDMA) modes, are especially susceptible to cable integrity
problems. If the cable is too long, you can experience data corruption and other errors
that can be maddening. This is manifested in problems reading from or writing to the
drive. In addition, any drive using UDMA Mode 5 (66MBps transfer rate), Mode 6
(100MBps transfer rate), or Mode 7 (133MBps transfer rate) must use a special, higher-
quality 80-conductor cable. Ialso recommend this type ofcable ifyourdrive is runningat
UDMAMode2(33MBps)orslowerbecauseitcan'thurtandcanonlyhelp.Ialwayskeep
a high-quality 80-conductor ATA cable in my toolbox for testing drives where I suspect
cable integrity or cable length problems.
Figure 7.5
shows the typical ATA cable layout
and dimensions.
Figure 7.5
PATA (IDE) cable, with 40-pin connectors and either 40- or 80-conductor cables (additional
wires are grounded in 80-conductor versions).
