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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