This appendix describes the Small Computer Systems Interface (SCSI). Topics covered in this appendix include:
There are two micro-miniature SCSI ports on the back panel of a DSPP. The SCSI connectors have 50 pins divided into two rows. You can connect the DBP your system in two ways - direct connection or daisy chain.
If fast SCSI devices and old-style connectors must be used in the same system, the old-style connectors should be connected to a separate SCSI port that doesn't contain fast SCSI devices. Do not connect fast SCSI devices and old- style connectors in the same daisy chain.
Old style connectors can be identified by a 3-row 50-pin D connector or a 50-pin ribbon style connector.
You can connect the DSPP to your system in two ways - direct connection or daisy chain. Connecting the SCSI cable of the DSPP to the SCSI port of your system is a direct connection. Connecting the SCSI cable of the DSPP to the SCSI port of another SCSI device is a daisy chain.
Use direct connection when you are connecting the first SCSI device in the SCSI bus to the computer system: connect one end of the SCSI cable to one of the SCSI ports of the peripheral device, and the other end of the SCSI cable to the SCSI port of the computer system. If needed, connect a regulated SCSI terminator to the other SCSI port of the peripheral device, as illustrated in Figure B-1.
Figure B-1 Example of a Direct Connection
If you installed an SBus card with an additional SCSI port in the computer system, you can connect the DSPP to the SCSI port of the SCSI card.
SCSI devices can be daisy chained. A daisy chain is a means of connecting a number of devices to a system. A SCSI cable connects the system to the nearest of the devices, and then a separate SCSI cable connects the first device to the second device. Another cable connects the second to the third and so forth.
A daisy chain allows a single port on the system to connect to more than one device. If you want more than one device on a bus, you will need to daisy chain.
Caution - Devices with the old-style connectors (3-row 50-pin D connectors or 50-pin ribbon connectors) must not be used on the same bus (daisy chained) with fast SCSI devices.
If you connect SCSI devices to your system in this manner, connect the terminator supplied with the DSPP to the unused SCSI port on the back panel of the last device in the daisy chain, as shown below:
Figure B-2 Example of a Daisy Chain Connection
You must attach a SCSI terminator to the SCSI port at the end of the SCSI bus. Recent model Sun systems and peripherals (including the SunCD Plus DSPP) are supplied with new regulated SCSI terminators. Previously, Sun supplied standard SCSI terminators. The new terminators provide the improved impedance matching required for fast SCSI. A terminator holds the bus at a predetermined signal level when the bus is not active and maintains impedance matching. All SCSI systems must be terminated at the first and last units attached to the SCSI bus. A terminator is built in to all SBus SCSI cards and to all host systems. (So in most cases, the system terminates one end of the bus.)
Figure B-3 Regulated and Standard SCSI Terminators
Follow these SCSI termination rules:
If Fast SCSI devices and old-style connector devices must be used in the same system, the old-style connector devices should be connected to a separate SCSI port that contains no Fast SCSI devices. The mixing of Fast SCSI devices and old-style connector devices in the same daisy chain is not recommended.
A bus is a signal route to which several parts of a computer system may be connected so that signals can pass between them. The total length of a SCSI bus includes:
The maximum SCSI bus length is 20 feet (6 meters). Reliable operation is guaranteed only up to the maximum SCSI bus length of 6 meters.
Table B-1 lists the SCSI cable lengths and the internal SCSI buses for the DSPP and your system. When connecting the DSPP to your system, find the total SCSI bus length for your configuration. To do this, add the cable and internal bus lengths for the system and each device. This total length must be less than 20 feet (6 meters).
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Devices and Cables SCSI Bus Length Inches Meters --------------------------------------------------------------------------
Devices, Internal Cables:
DSPP 0.3 11.81
SPARCstation 1, 2, IPC, IPX 0.5 19.7
SPARCstation 1+ 0.6 23.6
SPARCstation 10 0.9 35.43
SPARCstation SLC and ELC 0.9 35.43
SPARCserver 630* 2.8 110.2
SPARCserver 670** 2.5 98.4
External SCSI Cables:
DSPP Cable
(to connect to a desktop system or to daisy
chain a second DSP to the first on a 630 or 670)
0.8 31.5
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This totals 2.7 meters of cable, less than the 6 meter maximum for each SCSI bus.
This totals 3.1 meters of cable, less than the 6 meter maximum for each SCSI bus.
This totals 2.7 meters of cable, less than the 6 meter maximum for each SCSI bus.
This totals 4.7 meters of cable, less than the 6 meter maximum for each SCSI bus.
If the SCSI bus length exceeds 6 meters, install some of the devices on additional SCSI buses by installing an SBus SCSI Host Adapter card with desktop systems or an SBE/S SBus card with deskside or rack systems. The SBus SCSI Host Adapter card provides an additional SCSI port (SCSI bus) for your system. The SBE/S SBus card provides an additional SCSI port and an Ethernet port.
When you insert an SBus SCSI Host Adapter card into your system, the SCSI bus length total does not include the internal cable length of the system, listed in Table B-2. For example, if you have a SPARCstation IPC and are connecting two Desktop Storage Modules and two DSPPs to the SBus SCSI Host Adapter card of the system, you need to add the following cable lengths:
This totals 4.4 meters of cable length, less than the 6 meter maximum for each SCSI bus. Note that you do not include the length of the internal cable of the SPARCstation IPC (0.5 meters).
Additional SCSI buses, SCSI bus 1, 2, 3, and 4 are named based on the order they are found by the OpenBoot PROM when probing SBus slots. SBus slots are probed in this order: on-board, slot 0, slot 1, slot 2, slot 3.
For example, if the first SBE/S SBus card is in slot 2, when the system probes
the SBus slots, it begins probing the on-board SCSI bus, then SBus slot 1, then
SBus slot 2, and so on. Because slot 2 contains the first SBE/S SBus card, this is
SCSI bus 1. As Table B-2 illustrates, SCSI bus 1 supports disk, tape, and
CD-ROM drives.
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SCSI Bus Number Device -------------------------------------------
SCSI bus 1, first SBE/S SBus card Disk
Tape
CD-ROM
SCSI bus 2, second SBE/S SBus card Disk
SCSI bus 3, third SBE/S SBus card Disk
Tape
CD-ROM
SCSI bus 4, fourth SBE/S SBus card Disk
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