Not only is the Diagnostic Terminator the best ACTIVE Terminator on the market, it is also a
diagnostic analyzer that indicates where SCSI problems originate. The Active Diagnostic
Terminator is a diagnostic tool that can save you countless hours when diagnosing your SCSI
system. The four indicator LEDs show you what is happening on the SCSI Bus at all times.
Active termination is considered the best terminator solution for SCSI-2. Since it regulates the SCSI
Bus you have a much higher degree of reliability. The terminators active regulation maintains a
constant 2.85 volts while sourcing current to the signal lines at 24ma. This stable environment helps
create safer more reliable data-transfers and offers a higher immunity to noise.
The Active Diagnostic Terminator also incorporates 20u” gold connectors and contacts to improve
on conductivity and reduce inductive mismatches.
When plugging in the Terminator make sure all power is turned off. Damage may occur if you plug
in or remove SCSI devices while the power is turned on.
Termination Power (TRM)
The Termination Power Indicator should always be on. This indicator shows that Termination
Power is being supplied to pin 38 on the SCSI cable. The SCSI Bus will not operate properly if this
light is not on. The SCSI specification does not require all targets to supply power to this line and
should the host (initiator) lose the ability to supply power to the bus, data-transfers will no longer be
possible. Some older hosts (initiators) did not supply termination power and relied on the targets to
do this. This produced another problem when no one supplied termination power. Today most
hosts and targets supply this power and the problem has been remedied.
Select Line (SEL)
The Select Line indicates when a device has been selected and is either receiving or sending
information to the host. This LED is on whenever there is activity on the SCSI Bus. The Select Line
is on in conjunction with the ACK and REQ lines and should be blinking as the state of the SCSI
Request Line (REQ)
The Request Line is considered a clock line and it operates at very high speeds. It is critical to the
operation of the SCSI bus and when operating seems to be dim because of the speed in which this
line is turning on and off. The line represents the target requesting a response from the host (initiator).
Acknowledge Line (ACK)
The Acknowledge Line is also considered a clock line. It indicates that the host (initiator) is
responding to the targets request. The LED is also dim in normal use due to the high speed of this
clock line. Proper operation is indicated by a dim LED when there are data-transfers or when the
SCSI Bus is active.
The Active Diagnostic Terminator can tell you the state of the SCSI Bus after a computer crash. If
your computer crashes, DO NOT TURN OFF THE POWER until you examine the LED Indicators
on the Active Diagnostic Terminator. Table 2 lists the conditions of the SCSI Bus.
Key to Diagnostic LED Indicators
|Activity is on the SCSI Bus.|
|Termination Power is supplied on the SCSI Bus.This is the|
proper status of the SCSI Bus during a bus free state.
|The target is requesting a response from the initiator.|
|The initiator is acknowledging the targets request.|
|The target device is hanging the SCSI Bus.|
|The initiator is hanging the SCSI Bus.|
|The initiator is hanging the SCSI Bus.|
|The target is waiting for the next command from the initiator,|
or the target is reconnecting and hanging the SCSI Bus.
|No activity on the SCSI Bus and there is no Termination|
Power… power is off.
System is locked.
|The target is waiting for the next command from the initiator.|
Tips on Detecting Errors
The Active Diagnostic Terminator indicators give you a starting point on what to look for when
something goes wrong. To become familiar with its operation, it is recommended that you connect
the Diagnostic Terminator to a known working system and learn what the indicators do during
different states of SCSI Bus activity.
The main states to become familiar with are the following:
- When you initially boot the computer from the SCSI drive.
- When nothing is going on, the computer is idle, and nothing is being transferred via the SCSI Bus.
- When you are writing a file to a target device.
- When you are reading information from a target device.