General Considerations; Connecting Scsi Devices - Adaptec AHA-3980 Quick Reference Installation Manual

Do not replace the chassis cover or reconnect the
power yet!
5

Connecting SCSI Devices

You can attach internal devices to Channel A, B, or
C. External devices must attach to Channel A, which
is the only channel with an external connector.
Remember, each channel on an AHA-3980 or
AHA-3985 supports up to seven 8-bit devices. If you
attach one SCSI device to the internal connector of
Channel A, for example, you can attach up to six
devices to the external connector—a total of seven
devices on the channel. On an AHA-3980W or
AHA-3985W, each channel supports up to 15 devices
—either 16-bit devices alone or a combination of
16-bit and up to seven 8-bit devices.
Caution:
single-ended SCSI devices. Do not connect dif-
ferential SCSI devices to the adapter. To deter-
mine the device type, read the device
documentation or contact your vendor.

General Considerations

When you attach the SCSI devices, remember the fol-
lowing constraints:
If you combine 8-bit and 16-bit devices on an
external AHA-3980W or AHA-3985W channel,
you must attach the 8-bit devices after the 16-bit
devices; once you step down to an 8-bit device,
you cannot step back up to a 16-bit device. You
need a 68-pin-to-50-pin connector to attach the
last external 16-bit device to the first 8-bit device.
On each channel, the total length of cabling (inter-
nal and external) should not exceed
– three meters (9.8 feet) if you use Fast SCSI data
transfer rates such as the default rate (see Maxi-
mum Sync Transfer Rate in the table on
page 8)
AHA-398x adapters support only
4