With single channel and multi-channel wide SCSI host adapters like the 2940UW and 3940UW becoming more prevalent, users are running into situations where they must mix their existing narrow 8-bit SCSI devices with 16-bit wide SCSI devices. Cable converters and adapters are available in the marketplace to assist users to integrate these 8-bit narrow and 16-bit wide devices. However, users must beware that haphazardly mixing these narrow and wide devices on the same SCSI bus can cause termination and possible data corruption problems. This document will describe some of the cable converters and adapters available and then provide scenarios of how narrow and wide devices should be placed on the SCSI bus to avoid the termination and potential data corruption problems. Adaptec provides some of these converters and adapters for use with Adaptec's wide SCSI host adapters. A listing of the Adaptec cable kits is provided at the end of this document.
68 Pin to 50 Pin Cable : This cable provides a 68 pin wide male connector at one end and a 50 pin Centronics male connector on the other end. Typically, the high data byte originating at the 68 pin end is left floating and unterminated. Adaptec does not supply this cable. (See Figure A)
68 Pin to 50 Pin Adapter : This adapter comes in two flavors. One provides active termination for the high data byte while the other leaves the high data byte unterminated. The adapter provides a 68 pin male connector on one end and a 50 pin high density female connector at the other end. Users can order this adapter with active termination for the high data byte from Adaptec. The Adaptec part name for this adapter is ACK-68P-50P-E ( PN # 943000). (See Figure B)
68 Pin to 50 Pin Converter : This converter allows narrow devices to attach to an internal wide 68 pin ribbon cable. The high data byte is not terminated. Therefore wide devices can be placed on the SCSI bus after the narrow device. The converter has a 68 pin female connector and a 50 pin female connector. The Adaptec part name for this converter is ACK-68p-50p-I (PN # 962700). (See Figure C)
When users are deciding which cable converter or adapter they need, the two major factors to consider are the termination setting available on the SCSI host adapter and the types of SCSI devices they have. The next section of this document will describe some typical Adaptec Wide SCSI host adapters and some narrow and wide internal and external SCSI devices. The document will then use this set of SCSI devices to illustrate how the external 68 to 50 pin adapter, cable, and internal converter can be used to mix wide and narrow SCSI devices.
Devices (Wide SCSI Host Adapters, Wide and Narrow SCSI Peripherals)
2940W, 2940UW : Wide SCSI Host Adapter with internal 68 pin
(female), 50 pin (male) , and external 68 pin (female) connector. Note :
Only two out of the three connectors can be used at the same time else
SCSI-2 stub length (.1 Meter) specification would be violated.
Termination
Option : Autoterm (2940UW only), High = OFF Low = OFF, High = ON Low = OFF,
High = ON Low = ON
3940W, 3940UW : Wide Dual Channel Host Adapter with two internal
68 pin (female) and one external 68 pin (female) connector.
Termination
Option : Autoterm (3940UW Only), Enable (High = ON, Low = ON), Disable (High =
OFF, Low = OFF)
Internal Narrow 8-bit (50 pin male connector)
External Narrow 8-bit (50
pin Centronics female connector)
Internal Wide 16-bit (68 pin female
connector)
External Wide 16-bit (68 pin female connector)
The 68 pin to 50 pin adapters and cables without termination for the high data byte allow users to attach 8-bit (Narrow) external devices to a wide SCSI host adapter. (See Figure D)
User can not mix external wide and narrow devices when using these adapters or cables. The high data byte would not be properly terminated.
If users have both internal wide devices and external narrow devices, the SCSI host adapter must allow users to turn termination Off for the low data byte and On for the high data byte at the host adapter. If this option is not available with the adapter then the user MUST use the 68 pin to 50 pin adapter with termination for the high data byte. (See Figure E )
The 68 pin to 50 pin adapter with active termination for the high data byte works in all scenarios. The adapter can be connected to the external connector off the wide SCSI host adapter or connected to the last wide external device on the SCSI bus. (See Figure F )
The 68 pin to 50 pin converter allow users to place internal 8-bit (Narrow) devices on a wide internal cable. (See Figure G ) The only restriction on its usage is that a narrow device using this converter should not be the last device on the SCSI bus. If a narrow device was the last device then the high data byte would not be properly terminated. There are internal wide cables available in the market place that provide an active terminator at the end of the cable. A user with this cable will not have to worry about the placement of narrow devices attached to a wide internal SCSI cable. Adaptec provides this cable ACK-W2W-5IT (PN# 973100).
ACK-68P-50P-E (943000) Fully electrically
terminated external adapter to convert an external 68 pin connector to 50 pin
high density connector.
ACK-68p-50p-I (962700) An adapter that
converts a 68 pin connector to a 50 pin connector. For users of Wide SCSI host
adapters to connect their 8-bit devices to 16-bit connector on an internal wide
ribbon cable. No termination for high byte. For use with 2940W, 2940UW,
3940W and 3940UW host adapters.
ACK-68I-68E (972900)This kit allows users
to use an internal wide SCSI connector as an external wide SCSI connector. The
0.45 meter cable provides an internal 68 pin male connector and an external 68
pin female connector. Users must have an external vacant slot in their PC to
use this kit.
ACK-50I-50E (950600) This kit allows
users to use an internal narrow SCSI connector as an external narrow SCSI
connector. The 0.4 meter cable provides an internal 50 pin female connector
and a high-density external 50 pin female connector. Users must have an
external vacant slot in their PC to use this kit.
ACK-W2W-5IT (973100) This internal
68-pin high density wide ribbon cable supports 4 devices + the SCSI host
adapter. The end of the 1.4 meter cable is an active terminator that terminate
the wide SCSI bus.
To order Adaptec SCSI cables, call 800-442-SCSI (7274) or 408-957-SCSI (7274), M-F: 6:00 a.m. to 5:00 p.m., Pacific Time.