Macintosh Centris 650 Specifications download pdf

DV 15 - SCSI Termination Page: 1

NOTE: This Technical Note has been retired. Please see the Technical Notes page for current documentation.

CONTENTS

Why Is the Terminator After Sarah Connor?

How to Stop the Terminator

External Termination

You're Terminated

Macintosh Quadra Termination

PowerBook Termination

PowerBook Duo Termination

Termination Outlined for Each Macintosh

References

Change History

Downloadables

This Technical Note discusses SCSI

termination on the Macintosh, including the

new rules of termination that are necessary

with the advent of the high-speed Macintosh

IIfx.

Updated: [May 01 1992]

Why Is the Terminator After Sarah Connor?

One of the features of the now obsolete Macintosh IIfx was a new SCSI chip that provides SCSI data transfer rates up to 3

megabytes per second, faster than any Macintosh model prior to the Macintosh Quadra. To achieve these transfer rates,

components on the Macintosh IIfx logic board were smaller and faster, requiring different termination configurations

from those of previous Macintosh models.

The Macintosh IIfx requires the use of a combination of the following three new termination parts. Users need to use these

parts instead of existing SCSI termination parts to configure a Macintosh IIfx with SCSI devices. The Macintosh Quadra does

not require special termination as the Macintosh IIfx does, but it does have some special rules of its own and these are

discussed in a later section.

Apple SCSI Cable Terminator II: The Apple SCSI Cable Terminator II is a revised external terminator for the

Macintosh IIfx. All finished goods Macintosh IIfx systems ship with this terminator in the box. It is easily recognized

because of the black color. Under no circumstances should one use more than a single Apple SCSI Cable Terminator II on an

external SCSI chain--doing so may damage the logic board.

Internal SCSI Termination Block: The Internal SCSI Termination Block provides internal termination resistance for

Macintosh IIfx systems without internal hard drives. All finished goods systems shipping without internal hard drives

have the Internal SCSI Termination Block installed.

Internal SCSI Filter: The Internal SCSI Filter provides termination capacitance for internal Macintosh IIfx hard

drives that shipped prior to March 19, 1990. All finished goods systems shipping without internal hard drives have the

Internal SCSI Filter installed.

The new termination configurations are simple, and you can remember them with a single rule: Macintosh IIfx systems

with external SCSI chains require a terminator at both ends of the SCSI chain. One is internal to the system, while the

second is external, located at the end of the chain.

The reason for the new terminator is that on the Macintosh IIfx and future hardware, the SCSI controller chip is a 2

micron part, which makes it very fast. One of the results of this speed is that the chip now thinks that glitches in the /REQ

line are real signals. This problem is not likely to occur on all of the Macintosh IIfx machines, but if you have a problem

with your hard drive not getting mounted on the new machine, you should try a new terminator first. The symptom is more

likely to show up on machines with several (three or more) external SCSI devices attached to the computer and long

strands of SCSI cables. Figure 1 illustrates the old-style terminator with the signal showing the spike propagation.

Figure 1 - Old-Style Terminator (Gray)

1 2 3 4 5

Summary of Contents

Page 1 - CONTENTS

DV 15 - SCSI Termination Page: 1NOTE: This Technical Note has been retired. Please see the Technical Notes page for current documentation. CONTENTS W

Page 2 - PowerBook Termination

DV 15 - SCSI Termination Page: 2Basically, if a majority of the data lines change state at once, there is a sudden drain on the TPWR line, which isres

Page 3 - PowerBook Duo Termination

DV 15 - SCSI Termination Page: 3There are two important points that one must be aware of when it comes to termination on the Macintosh PowerBookcomput

Page 4

DV 15 - SCSI Termination Page: 4* "...an active termination circuit automatically terminates the [internal device] when it is the last device on

Page 5 - Change History

DV 15 - SCSI Termination Page: 5Back to topReferencesMacintosh Technical Note "Fear No SCSI" Back to topChange History01-April-1990 Original

Macintosh Centris 650 Specifications

Browse online or download Specifications for PC/workstation barebones Macintosh Centris 650. Macintosh Centris 650 Specifications User Manual

Summary of Contents

More documents for PC/workstation barebones Macintosh Centris 650

Comments to this Manuals

Macintosh Centris 650 Specifications

Browse online or download Specifications for PC/workstation barebones Macintosh Centris 650. Macintosh Centris 650 Specifications User Manual

Summary of Contents

More documents for PC/workstation barebones Macintosh Centris 650

Comments to this Manuals

Related products and manuals for PC/workstation barebones Macintosh Centris 650