Black Box SCSI Switch II User manual

1000 Park Drive • Lawrence, PA 15055-1018 • 724-746-5500 • Fax [phone]
© Copyright 1996. Black Box Corporation. All rights reserved.

CUSTOMER
SUPPORT
INFORMATION
Order toll-free in the U.S.: Call 877-877-BBOX (outside U.S. call 724-746-5500)
FREE technical support 24 hours a day, 7 days a week: Call 724-746-5500 or fax [phone]
Mailing address: Black Box Corporation, 1000 Park Drive, Lawrence, PA 15055-1018
Web site: www.blackbox.com • E-mail: [email protected]
DECEMBER 1996
SW845A-R2
SW845AE-R2
SCSI Switch II
SCSI Switch II
Power Port B Port C
Port A

2
SCSI SWITCH II
TRADEMARKS USED IN THIS MANUAL
UL is a registered trademark of Underwriters Laboratories Incorporated.
All applied-for and registered trademarks are the property of their respective
owners.

3
FCC STATEMENT
FEDERAL COMMUNICATIONS COMMISSION
AND
INDUSTRY CANADA
RADIO FREQUENCY INTERFERENCE STATEMENTS
This equipment generates, uses, and can radiate radio frequency energy and if not
installed and used properly, that is, in strict accordance with the manufacturer’s
instructions, may cause interference to radio communication. It has been tested
and found to comply with the limits for a Class A computing device in accordance
with the specifications in Subpart J of Part 15 of FCC rules, which are designed to
provide reasonable protection against such interference when the equipment is
operated in a commercial environment. Operation of this equipment in a
residential area is likely to cause interference, in which case the user at his own
expense will be required to take whatever measures may be necessary to correct
the interference.
Changes or modifications not expressly approved by the party responsible
for compliance could void the user’s authority to operate the equipment.
This digital apparatus does not exceed the Class A limits for radio noise emission from
digital apparatus set out in the Radio Interference Regulation of Industry Canada.
Le présent appareil numérique n’émet pas de bruits radioélectriques dépassant les limites
applicables aux appareils numériques de la classe A prescrites dans le Règlement sur le
brouillage radioélectrique publié par Industrie Canada.

4
SCSI SWITCH II
NORMAS OFICIALES MEXICANAS (NOM)
ELECTRICAL SAFETY STATEMENT
INSTRUCCIONES DE SEGURIDAD
1. Todas las instrucciones de seguridad y operación deberán ser leídas antes de
que el aparato eléctrico sea operado.
2. Las instrucciones de seguridad y operación deberán ser guardadas para
referencia futura.
3. Todas las advertencias en el aparato eléctrico y en sus instrucciones de
operación deben ser respetadas.
4. Todas las instrucciones de operación y uso deben ser seguidas.
5. El aparato eléctrico no deberá ser usado cerca del agua—por ejemplo, cerca
de la tina de baño, lavabo, sótano mojado o cerca de una alberca, etc..
6. El aparato eléctrico debe ser usado únicamente con carritos o pedestales que
sean recomendados por el fabricante.
7. El aparato eléctrico debe ser montado a la pared o al techo sólo como sea
recomendado por el fabricante.
8. Servicio—El usuario no debe intentar dar servicio al equipo eléctrico más allá
a lo descrito en las instrucciones de operación. Todo otro servicio deberá ser
referido a personal de servicio calificado.
9. El aparato eléctrico debe ser situado de tal manera que su posición no
interfiera su uso. La colocación del aparato eléctrico sobre una cama, sofá,
alfombra o superficie similar puede bloquea la ventilación, no se debe colocar
en libreros o gabinetes que impidan el flujo de aire por los orificios de
ventilación.
10. El equipo eléctrico deber ser situado fuera del alcance de fuentes de calor
como radiadores, registros de calor, estufas u otros aparatos (incluyendo
amplificadores) que producen calor.
11. El aparato eléctrico deberá ser connectado a una fuente de poder sólo del
tipo descrito en el instructivo de operación, o como se indique en el aparato.

5
NOM STATEMENT
12. Precaución debe ser tomada de tal manera que la tierra fisica y la polarización
del equipo no sea eliminada.
13. Los cables de la fuente de poder deben ser guiados de tal manera que no
sean pisados ni pellizcados por objetos colocados sobre o contra ellos,
poniendo particular atención a los contactos y receptáculos donde salen del
aparato.
14. El equipo eléctrico debe ser limpiado únicamente de acuerdo a las
recomendaciones del fabricante.
15. En caso de existir, una antena externa deberá ser localizada lejos de las lineas
de energia.
16. El cable de corriente deberá ser desconectado del cuando el equipo no sea
usado por un largo periodo de tiempo.
17. Cuidado debe ser tomado de tal manera que objectos liquidos no sean
derramados sobre la cubierta u orificios de ventilación.
18. Servicio por personal calificado deberá ser provisto cuando:
A: El cable de poder o el contacto ha sido dañado; u
B: Objectos han caído o líquido ha sido derramado dentro del aparato; o
C: El aparato ha sido expuesto a la lluvia; o
D: El aparato parece no operar normalmente o muestra un cambio en su
desempeño; o
E: El aparato ha sido tirado o su cubierta ha sido dañada.

6
SCSI SWITCH II
Contents
Chapter Page
1. Specifications ............................................................................................. 7
2. Introduction ............................................................................................... 8
2.1 The Complete Package ....................................................................... 8
2.2 Description .......................................................................................... 9
2.3 Caring for the Switch ........................................................................ 10
3. Installation ................................................................................................ 11
3.1 Preinstallation Guidelines ................................................................ 11
3.2 Installing the Switch .......................................................................... 11
4. Operation ................................................................................................. 12
5. Troubleshooting ...................................................................................... 13
5.1 Common Problems ........................................................................... 13
5.2 Contacting Your Supplier ................................................................. 15
5.3 Shipping and Packaging ................................................................... 15
6. Technical Details ..................................................................................... 16
6.1 Bus Length ........................................................................................ 16
6.2 Termination ...................................................................................... 16
6.3 Termination Exceptions ................................................................... 17

7
CHAPTER 1: Specifications
1. Specifications
Compliance — UL®, CSA, FCC Part A, CE
Protocol — Synchronous and asynchronous
Standards — SCSI-1, SCSI-2, and SCSI-3
Interface — Single-ended
Termination — All branches must be terminated externally
SCSI ID — None
User Controls — (3) Pushbuttons for branch selection (Port A, B, or
C)
Indicators — (1) Power, (3) Branch-connected LEDs
Connectors — (1) P5 2.1-mm female power jack, (4) high-density
68-pin SCSI-3
Enclosure — ABS plastic
Operating
Temperature — 32 to 158˚F (0 to 70°C)
Storage
Temperature — –4 to +212˚F (-20 to +100˚C)
Humidity — 10 to 95%, noncondensing
Maximum Altitude
Tolerance — 15,000 feet (4570 m)
Power — SW845A-R2: 120 VAC wallmount, 9 VDC @ 500 mA;
SW845AE-R2: 100–260 VAC wallmount, 9 VDC @
500 mA
Size — 2.3"H x 8.1"W x 4.3"D (5.8 x 20.6 x 10.9 cm)
Weight — 1.4 lb. (0.6 kg)

8
SCSI SWITCH II
2. Introduction
The SCSI Switch II is a SCSI-bus-sharing switch that connects multiple
combinations of host and target devices to each other. In situations in which
more than one user want to share a SCSI device, the SCSI Switch II eliminates
the hazards associated with “hot-swapping” bus cables: Instead of users
shutting down a system to plug and unplug cables, the SCSI Switch II switches
the SCSI bus between them cleanly and safely. The Switch’s built-in logic
monitors bus activity and ensures that data transfer will not be interrupted. Its
compact size allows the SCSI Switch II to be set up for many different
configurations.
2.1 The Complete Package
You should have received these items with your SCSI Switch II:
• The SCSI Switch II itself,
• The Switch’s AC power supply, and
• This manual.
If you didn’t receive everything, contact your supplier immediately.
The basic SCSI Switch II is ready to install and use in almost any SCSI
system with a “single-ended” interface. (The Switch does not support the
“differential” interface.) The SCSI adapter cables are necessary to connect the
Switch to standard SCSI-1 or SCSI-2 equipment on with telco connectors or
high-density 50-pin connectors on the branch buses.

9
CHAPTER 2: Introduction
2.2 Description
With the SCSI Switch II, you can switch between one “main” SCSI bus and
three “branches.” Both the main bus and the branch buses may have any
combination of SCSI initiators (host computers) and targets (disk drives,
scanners, tape drives, etc). There is no difference between the main bus and
the three branches except for the way they are routed through the Switch:
Figure 2-1. Routing of Main Bus and Thre Branch Buses.
The SCSI Switch II supports the common “single-ended” SCSI interface.
The main-bus connector on the back of the SCSI Switch II (labeled INPUT)
is a female high-density 68-pin receptacle. There are three branch-bus
connectors (labeled A, B, and C). Each one is a high-density 68-pin
connector.
Main
Bus
Branch
Buses
A
B
C

10
SCSI SWITCH II
2.3 Caring for the Switch
The SCSI Switch II is a completely electronic switch. It has been designed for
durability and ease of maintenance, but some care should be taken when
handling it. Please do not expose the Switch to high humidity or extreme
electrical fields. Also, though the Switch can withstand a lot of heat, keeping it
away from high temperatures will extend its life.
When you install the SCSI Switch II, as with all computer devices, please
take precautions against static electricity. Before handling the Switch,
discharge any static electricity you might have accumulated: touch a
grounded piece of metal such as a computer cabinet, a metal table, or a
power outlet’s metal cover plate.

11
CHAPTER 3: Installation
3. Installation
Install the SCSI Switch II as a standalone desktop unit. The Switch gets its
power through its external power supply.
3.1 Preinstallation Guidelines
Before you install the SCSI Switch II, make sure that the total length of any
of the three possible data paths does not exceed 6 meters (19.7 feet) for 8-bit
SCSI-1 and SCSI-2 or 3 meters (9.8 feet) for 16-bit SCSI-2 and SCSI-3. This is
the maximum allowed by SCSI specification, and it is fully attainable; though
“active” (automatic) switches introduce load on the bus and reduce the
maximum length of cable you can run, the SCSI Switch II is a “passive” device
and does not subtract from this limit.
When you attach a SCSI adapter cable to the Switch, you must make sure
that Pin 1 on the cable’s connector goes to Pin 1 on the Switch’s connector.
3.2 Installing the Switch
To set up the SCSI Switch II on a desktop or otherwise outside of a system
cabinet, follow these steps:
1. Find a clear, uncluttered location away from obvious dangers, such as
liquids and high temperatures.
2. Attach the main host bus cable to the connector marked “INPUT.” Make
sure Pin 1 on the cable connector is aligned with Pin 1 of the Switch
connector.
3. Attach the branch bus cables to the respective branch connectors (“A,”
“B,” and “C”), using SCSI adapter cables if necessary. Again, make sure
Pin 1 on each cable connector is aligned with Pin 1 on the corresponding
Switch connector.
4. Plug the input cord of the Switch’s power supply into the power jack on
the rear of the Switch, then plug the power supply into a working outlet.

12
SCSI SWITCH II
4. Operation
The SCSI Switch II begins operating as soon as it has been connected to a
working power source through its power supply; it has no On/Off switch.
(The Switch is in no danger if power is removed or goes down, but data may
be lost if this happens while the SCSI system is operating.)
The main SCSI bus is always connected to one of the three branch buses.
You control which of the branch buses is connected by pressing the
pushbuttons (labeled Ports A, B, and C) on the SCSI Switch II’s front panel.
When you select a new branch, the SCSI Switch II waits to connect to the new
branch until it is safe to disconnect from the old branch (data transmission to
and from the old branch has stopped).
Once you’ve plugged in the switch, all of the LEDs will light for one second
to signal a successful reset. The LED for the last branch connected will light
up. If it blinks rapidly, it’s transmitting data. If it stays constantly lit, there is
no data currently transmitting.
To switch branches, push the button labeled Port A, Port B, or Port C. If
a previous connection is still active (noted by a rapidly flickering port LED),
the Switch will flash the LED of the port you selected (approximately once
per second) until the bus currently transmitting is inactive for 8 seconds.
Then that branch is disconnected, and the branch you selected is connected.
The LED next to the branch you selected should be lit, and the LED of the
disconnected port should not be lit.
When power is restored to the SCSI Switch II after the power fails or the
Switch’s power is unplugged, the Switch will connect the main bus to the
branch bus last selected. If power is lost during a pending branch change, the
previous connection (the one that was still active when power was lost) is not
re-established unless you push the button for that branch’s position.

13
CHAPTER 5: Troubleshooting
5. Troubleshooting
If you encounter a problem when you install or operate the SCSI Switch II,
please review this section for likely causes and what to do if you eliminate
these possibilities but the problem remains.
5.1 Common Problems
Problem 1. LEDs are not lit:
Check whether the power supply is the one supplied with the SCSI Switch II.
You can use a different power supply, but it must have a rating of 9 or 12 volts
DC, 1 amp maximum with the positive terminal on the inside of the
connector. Also, check whether the power supply is connected to a live power
outlet.
Problem 2. Branch-indicator LED flashes constantly:
This is an indication that the main bus and the formerly selected branch bus
(the branch corresponding to the number on the front-panel display) are
busy with data traffic, but a different branch has been selected (button has
been pushed to a new setting). This condition will resolve itself when, after
traffic stops for at least eight seconds, the Switch disconnects the formerly
selected branch bus and connects the new branch.

14
SCSI SWITCH II
Problem 3. SCSI Switch II appears to be working, but SCSI device does not
respond properly to system:
If possible, remove the SCSI Switch II. Then, if the device with the problem is
on a branch bus, connect that branch directly to the main bus; if the problem
device is on the main bus, either terminate the unterminated end of the main
bus or connect the main bus to one of the three branch segments. Now try
the same type of communication with that device; if the communication
succeeds, contact your supplier, because either there’s something wrong with
your Switch or you’ve hit a SCSI bug.
If the communication still fails, try these measures:
• Check power to all SCSI devices.
• Check the ID codes of all devices throughout the system and correct any
conflicts. On the SCSI bus, no two devices may have the same ID. With the
SCSI Switch II in place, you may be connecting two bus segments that
have similar ID codes. (To check and reset ID settings on your SCSI
devices, please refer to the manuals supplied with those devices.)
• Check your SCSI cables. Make sure that all Pin 1 markers are matched
(no cables are connected backwards). Make sure that all cables are in
working order. Interchange cable segments to test in other locations as a
process of elimination.
• The terminators on that bus segment might be bad. Try swapping in
replacements.

15
CHAPTER 5: Troubleshooting
5.2 Contacting Your Supplier
If your SCSI Switch II seems to be malfunctioning, do not attempt to alter or
repair the unit. Call your supplier. The problem may be solvable over the
phone.
Before you call, make a record of the history of the problem. Your supplier
will be able to provide more efficient and accurate assistance if you have a
complete description, including:
• the nature and duration of the problem,
• when the problem occurs,
• the components involved in the problem and their SCSI ID numbers, and
• any particular application that, when used, appears to create the problem
or make it worse.
5.3 Shipping and Packaging
If you need to transport or ship your SCSI Switch II:
• Carefully package the Switch. We recommend that you use the original
container.
• If you’re shipping the Switch for repair, include its power supply. If you’re
returning the Switch, include both the power supply and this manual.
Before you ship, contact your supplier to get a Return Materials
Authorization (RMA) number.

16
SCSI SWITCH II
6. Technical Details
6.1 Bus Length
The single-ended SCSI interface provides for connections of up to 6 meters
(19.7 feet) in length for 8-bit SCSI-1 and SCSI-2 or 3 meters (9.8 feet) for 16-
bit SCSI-2 and SCSI-3. This means that no total bus length may be longer than
6 (or 3) meters between the two most distant devices. When you install the
Switch, be sure not to create any combination of bus segments longer than
the 6- (or 3-) meter maximum.
6.2 Termination
Termination resistor packs (“terminators”) are used to ensure proper signal
levels on the SCSI bus, and are essential for its operation. There are two types
of terminators, one for the more common “single-ended” interface, another
for the “differential” interface. The SCSI Switch II only supports single-ended
SCSI.
The first and last devices on a SCSI bus—and only those devices—should
have terminators installed. Thus, a SCSI bus should have two terminators, one
at each end.
The SCSI Switch II acts as a pass-through switch and introduces no unusual
termination effects, so when you plan a system with the SCSI Switch II and
three branch buses without independently operating SCSI initiators, handle
termination as if the SCSI Switch II is simply another connector. If a branch
bus won’t be operating while it’s disconnected from the main bus—it has only
target devices, or an initiator that will not transfer data when disconnected—it
can be terminated with only one terminator at the far end of the branch. The
main bus segment will always be connected to one branch segment, so if you
position a terminator at the end of the main bus farthest from the Switch, the
main bus will always be properly terminated, because the branch supplies the
second termination.

17
CHAPTER 6: Technical Details
When you check, install, or reposition terminators, please make sure that
they are pointed in the right direction, with Pin 1 properly aligned. Also, in
order for termination to work properly, there should be a termination-power-
source (“TERMPWR”) present. Some SCSI devices have a tiny fuse for the
termination-power line, which may be located very close to the termination
sockets: If you can see this fuse, TERMPWR should be present. If you can’t see
the fuse, however, this doesn’t necessarily mean that TERMPWR is absent.
Consult the manual for the SCSI device in question.
6.3 Termination Exceptions
This is the normal termination arrangement with the SCSI Switch II (the
wedge shapes represent terminators):
Figure 6-1. Normal Termaination.
An exception to the illustration above is the case where a branch bus may
have local data traffic even while it’s disconnected from the main bus—if the
branch has, for example, both a computer and a disk drive, and the computer
can operate the drive even when the main SCSI bus isn’t switched to that
branch.
Normally, termination should be placed at the two very ends of a SCSI bus.
For a SCSI Switch II system, this means one terminator at the end of the main
bus and one at the end of each branch bus. But if an unselected branch bus
can operate on its own, then it must have termination at both of its ends. So
imagine that we dutifully add a terminator to the near end of such a segment
Main
Bus
Branch
Buses

18
SCSI SWITCH II
to match the one on the far end. The only problem with this scenario is that
when you select that branch and the Switch links it to the singly terminated
main bus, the total number of terminators on the bus rises to three.
This violates SCSI rules and has little chance of working properly.
In such cases, special care should be taken to manage the bus
configuration. Termination should always be placed near the ends of the
overall SCSI bus. However, where a branch may have data traffic while
disconnected from the main bus, termination may be moved slightly to
accommodate the situation:
First, shorten the main bus so that it’s no longer than a few centimeters
(two or three inches). Then replace the termination normally found at
the end of the main bus with terminators the top of each branch, no farther
than another few centimeters (another two or three inches) from the SCSI
Switch II:
Figure 6-2. Alternate Termination.
As long as the main bus is short enough, and as long as the main bus has
only one or possibly two devices, these devices will be close enough to the
branch-top termination and the bus will probably operate correctly. However,
please note that such a configuration is still in violation of SCSI rules. This is
also not the intended use of the SCSI Switch II. The Switch is designed to
support “dead” branches only, in conformance with the nature of the SCSI
bus.
If termination is not properly configured, you may experience
unpredictable behavior or loss of data. For more information, please see
the documentation for your particular SCSI devices.
Main Bus
(Short, No
Termination)
Branch Buses (Long,
Both Ends Terminated)