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SCSI Bus Signal Converters

6.1 DWZZA Description

The following is a list of the features and functions of the DWZZA SCSI bus

signal converters:

• Converts two physical buses (a single-ended bus and a differential bus) into a

single logical bus.

Note

The 16-bit differential host or controller bus must be operating in the

8-bit mode.

• The length of the logical bus is equal to the length of the two physical buses.

• The logical bus has a total of eight device addresses (0 through 7).

• The converter does not use a SCSI device address.

• Establishes a physical connection between a 16-bit, differential bus operating

in the 8-bit mode and an 8-bit, single-ended SCSI device (communication

between the host and the SBB are 8-bit).

• Data transfers at rates of up to 10 million transfers per seconds (10

Megabytes/second

) are supported.

• The converter operation is transparent to both buses.

6.2 Installing SCSI Bus Signal Converters

The manner in which SCSI bus signal converters are installed is primarily based

upon the SCSI host.

Note

Unless otherwise stated, the DWZZA signal converters are installed in

the end-bus position. This requires that both the differential bus and the

single-ended bus be terminated within the DWZZA.

As shown in Figure 6–1 you would connect a host to the SBB shelf as follows:

• When using a single-ended host, you can connect the host SCSI controller or

adapter directly to the SBB shelf with a single ended cable. No DWZZA is

required for this conﬁguration.

• A differential host operating in the 8-bit mode can be connected directly to

the DWZZA.

• To create a logical bus longer than the single-ended physical bus, you would

install two DWZZAs, a DWZZA–AA, and a DWZZA–VA.

– The desktop model, the DWZZA–AA, is connected to the host with a

50-conductor, single-ended (SCSI–A) cable, such as a BC09D or BN21H.

This rate is supported only when at least one device supports the 10 MB/s transfer rate

and the bus has been designed as a fast bus.

6–2 SCSI Bus Signal Converters

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Digital Equipment Corporation Storage Works Guia do Utilizador Página 54