Troubleshooting SCSI Disk Mode

What is SCSI Disk Mode? How would I set my PowerBook up for it?

Which PowerBook models support SCSI Disk Mode?

Since PowerBooks have internal termination, why do I need an external terminator when using SCSI Disk Mode?

What is SCSI Disk Mode? How would I set my PowerBook up for it?

SCSI Disk Mode (in the PowerBook's ROM) allows you to use a PowerBook as an external SCSI device. You can then connect the PowerBook to any other SCSI-equipped Macintosh and transfer files directly from the desktop Macintosh to and from the PowerBook.

Preliminaries:
The two hard-drive volume names (the one on the desktop Macintosh and the one on the PowerBook) CANNOT be identical.

To use SCSI Disk mode, you need:
- The HDI-30 SCSI disk adapter, which plugs into the SCSI port of the PowerBook.
- A SCSI system cable and SCSI terminator.

Making the Connection:
The Macintosh User's Guide for Macintosh PowerBook computers contains instructions for making the connections between the PowerBook and various desktop Macintosh systems. Just as with any other SCSI device, both the PowerBook and the desktop Macintosh MUST BE POWERED OFF when the cable connections are made. Make sure your PowerBook is not in Sleep mode.

Activating SCSI Disk Mode:

Once you connect the cables, power up the PowerBook by pressing the appropriate key. The drive will then spin up.
Power up the desktop system. The PowerBook's hard drive should appear on desktop system's display (the PowerBook display will show a moving SCSI icon with the selected SCSI ID number.) In SCSI Disk Mode, treat the PowerBook like an external hard drive.

Exiting From SCSI Disk Mode:
To exit SCSI Disk Mode, press the PowerBook's Reset switch or the interrupt switch, or both together. This shuts down the PowerBook to allow removal of the SCSI Disk Mode adapter.

The next time you turn on the PowerBook, it will start up as usual.

Technical Notes:
You enter SCSI Disk Mode by starting the PowerBook with a special adapter plugged into the SCSI connector on the back of the computer. The ROM code checks for the presence of the SCSI Disk Mode adapter. If the adapter is absent, the ROM sets the SCSI address to seven (normal CPU SCSI address), and continues to start up normally. If the cable is present, the ROM checks the battery voltage to see if it's high enough to enter SCSI Disk Mode. The ROM then changes the hard disk address to the address stored in PRAM, sets backlighting to minimum, turns on the hard drive, and begins animating the screen. The SCSI Disk Mode ID number is set in the PowerBook control panel. The default is 1, but you can select any number from 1 to 6. This number is stored in parameter RAM (PRAM).

It's important to connect the SCSI Disk Mode adapter only when the PowerBook has been shut down. The firmware necessary to enter SCSI Disk Mode is executed only at startup. Because the SCSI Disk Mode firmware isn't executed when you connect the adapter during sleep, the SCSI bus potentially has two bus masters and two devices with SCSI ID 0, leading to potential data loss.

To prevent data loss in this situation, a modal warning dialog window appears and the menu bar isn't accessible. You have two options:

Disconnect the SCSI Disk Mode adapter. Removing the adapter removes the warning dialog box, and you can resume using the system. Although this procedure is counter to the suggestion of always making connections while the system is shut down, you can do it with no problems under these circumstances. You can then shut down the system from the menu bar.
Simultaneously press the Reset and Interrupt buttons. This shuts down the system, but all RAM data will be lost with no opportunity to save the data.

Which PowerBooks models support SCSI Disk Mode?

The SCSI Disk Mode feature exists on all PowerBook models except the PowerBook 140, 145, 145B, 150, and 170. Those PowerBooks which support the feature have it coded into their read-only memory (ROM).

You must use the appropriate SCSI cable for SCSI Disk Mode, the part number for the HDI-30 Disk Adapter cable is M2539LL/A. Similar cables are also available from third-party manufacturers (APS and System Connection both sell a switchable one).

You can distinguish the Disk Adapter cable from a standard SCSI cable by looking on the PowerBook end of the cable, there should be 30 pins. Regular PowerBook SCSI cables contain only 29 pins at the PowerBook end.

Since PowerBooks have internal termination, why do I need an external terminator when using SCSI Disk Mode?

All PowerBooks as well as the Macintosh Portable provide internal hard disk drive termination. The 1.3 KOhm pull-up resistor provides only a minimal amount of termination however. Therefore, even though the system has internal termination, it requires an external terminator when used in SCSI Disk Mode.

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