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Connecting 8 Bit and 16 Bit Devices

To Wide SCSI Adaptec Host Adapters

Mark E. Donaldson

Revised November 28, 2008 Page 1 of 4

Connecting 8-bit and 16-bit devices to an Adaptec wide host adapter is a straight-forward process once

the following basics are understood:

 Signal requirements of narrow devices

 Signal requirements of wide devices

 External converters and how they deal with termination

 Internal converters and how they deal with termination

Eight bit devices are also referred to as narrow devices and 16-bit devices are referred to as wide

devices.

Please note that in order to mix wide and narrow devices; a wide host adapter (2740W, 2742W, 2744W,

2940W, 2940UW Mac, 2944W, 2940UW, 3940W, 3940UW, 3940UW Mac, 3940UWD, 3944UWD) is

required.

Signal Requirements of Narrow Devices

Narrow devices require 50-pin inputs. The signals carried by these 50 pins can be represented as

follows:

The Low Byte is sometimes called the Low Data Byte.

Signal Requirements of Wide Devices

Wide devices require 68-pin inputs. The signals carried by these 68 pins can be represented as follows:

The High Byte is sometimes called the High Data Byte.

Adaptec External Converter (ACK-68P-50P-E)

In order to go from a 68-pin external connection to a 50-pin external connection, all that is required is

termination of the High Byte. This is what the ACK-68P-50P-E does.

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Connecting 8 Bit and 16 Bit Devices To Wide SCSI Adaptec Host Adapters Mark E. Donaldson Revised November 28, 2008 Page 1 of 4 Connecting 8-bit and

Connecting 8 Bit and 16 Bit Devices To Wide SCSI Adaptec Host Adapters Mark E. Donaldson Revised November 28, 2008 Page 2 of 4 An important consi

Connecting 8 Bit and 16 Bit Devices To Wide SCSI Adaptec Host Adapters Mark E. Donaldson Revised November 28, 2008 Page 3 of 4

Connecting 8 Bit and 16 Bit Devices To Wide SCSI Adaptec Host Adapters Mark E. Donaldson Revised November 28, 2008 Page 4 of 4 Internal Devices Ex

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Adaptec AHA-2740W Manuale Utente