Date: Thu, 21 Sep 1995 12:12:27 EDT

Subject: SCSI Issues

The following document contains information on using SCSI with the 2000, as well as specific sections dealing with computers and the 2000.

Here are some basic guidelines to follow when configuring a SCSI chain:

1. According to the SCSI Specification, the maximum SCSI cable length is 6 meters (19.69'). Users should limit the total length of all SCSI cables connecting external SCSI devices to Kurzweil products to 17 feet (5.2 meters). To calculate the total SCSI cable length one must add up the lengths of all SCSI cables, plus 8" for every external SCSI device connected.

2. The first and last device in the chain must be terminated.

Poor termination is a common cause of SCSI problems. If one installs an internal drive that is terminated, the termination resistors should be removed from the K2000 Engine Board. Having more than two terminators on the bus will overload the bus drivers, but this should not cause permanent damage to the hardware. Poor termination will corrupt that data on one's disk, however, as can bad SCSI cables.

For the K2000R, if it is not located at one end of a SCSI chain all internal termination, including the terminator resistor network on the K2000 Engine Board plus terminator resistors in the internal SCSI drive must be removed. It is much simpler to just make sure that the K2000 is at one end of the SCSI chain.

A note about active termination - The K2000 uses active termination of the SCSI bus. Active termination has some benefits over traditional passive termination. Some people have positioned active termination as a panacea for SCSI problems, but this is more hype than reality. Active terminators are available to be used at the end of one's SCSI chain and all APS SR2000 series external drives use internal active termination that can be switched on or off.

3. Each device in the chain (including int. hard drives) must have its own unique SCSI ID. The default K2000 ID is #6. Macintoshes use ID #7 & 0.

4. Use only true SCSI cables - high quality, twisted pair, shielded SCSI cable. Do not use RS432 or other non SCSI cables.

The majority of SCSI cables we've tested were poorly made and could cause damage data transferred to and from the disk. Nearly all the SCSI data problems Young Chang's engineering department has had have been due to bad cables that didn't twist pairs of wires properly. Correctly made SCSI cables have one ground wire for every signal wire and twist them together in signal/ground pairs. Cables made by APS Technologies (800.233.7550) are very good and are highly recommended. Good cables are essential to reliable data transfers to and from the disk drive.

5. One should buy all SCSI cables from a single source to avoid impedance mismatch between cables.

6. Theoretically all eight SCSI IDs can be used. However, feedback from users has shown us that many people have problems with more than 5-6 devices in a chain. If you have 7 or 8 devices and are having problems, the best bet is to make sure you have followed all of the previous information, especially with respect to cables.

7. Connect all SCSI cables before turning on the power on any equipment connected by SCSI cables.

8. Authorized service centers will remove termination from the K2000 when installing an internal drive, set its ID correctly, and terminate the drive.

9. When using a Macintosh, power up the K2000 and other devices first.

10. The K2000 file format is a proprietary format; no other device will be able to read or write a Kurzweil file.

11. The floppy disk format of the K2000 is DOS. The SCSI disk format is a proprietary form that is close to DOS, but it is not DOS. However, if you have version 3, the K2000 can read and write to a DOS formatted disk provided it was formatted on the PC with no partitions. If the drive is partitioned, the K2000 will see only the first partition.

12. It is possible to view, copy, move, name, delete files on a K2000 formatted floppy disk or DOS formatted removable media hard drive, with a PC or Macintosh running a DOS mounting utility program such as Access PC.

13. As long as the SCSI bus is properly terminated there is no way that a user can damage one's hardware simply by operating it. There are a few hazards K2000 users should be aware of, however:

The only damage that usually ocurrs to SCSI hardware comes from static electricity "zapping" SCSI connector pins when the cables are disconnected. The silver colored shell of the SCSI connector on the end of the cable is connected to ground and is safe to touch, but the brass colored pins inside eventually lead to the SCSI interface chip and are vulnerable. One should discharge static from one's body before touching SCSI connectors by touching the 1/4" jacks on the rear of the K2000 or another grounded metal object. Any devices connected to the SCSI bus should be turned off when plugging or unplugging SCSI cables.

If the K2000 is connected to a Macintosh or PC one should make sure that the computer cannot access a SCSI disk at the same time the K2000 does (see below for more info on this). Those who occasionally want to share a drive, but don't want to take any risks would be best served by disconnecting and connecting devices as needed. If you want to share drive(s) often and cannot constantly disconnect and reconnect devices make sure the Mac or PC is really done with the disk before using the K2000. One should quit or exit from all running programs and disable screen savers, email, network file sharing, and any INITs or TSR's that run in the background. If the computer and K2000 access the disk at the same time there will be no damage to the hardware, but the bits on the disk, K2000, and computer memory can easily be corrupted. One may not know that damage has been done to these bits until weird things start to happen for apparently no reason.

1. The Mac really does not like having another SCSI master on the bus (ie the K2000). It assumes that it owns the bus and it's drives, therefore it will not tolerate the situation where the K2000 is trying to talk to it's (the Mac's) disk. This suggests that you never want to select the ID of any drive mounted on the Mac's desktop. Even more fundamental is the problem that the Mac assumes that the bus is always free, so if it's OS tries to do anything via SCSI when the K2000 is doing anything via SCSI, the Mac will freak. The only solution is, wait until your Mac is completely idle before accessing SCSI from the K2000.

2. The Mac and the K2000 cannot share a Mac formatted drive in any way, with or without partitions. If you are using a drive with removable media, you can switch back and forth between a Mac formatted volume and a DOS formatted volume, if the Mac has the appropriate software which will allow it to access DOS formatted SCSI disks. If the disk is K2000 formatted (not DOS formatted), to prevent potential problems, you will need to unmount the drive from the Mac desktop before switching to a K2000 format volume. The Mac will basically ignore the volume if it's not Mac (or DOS) format, but once you insert a Mac format volume, the Mac owns it. Don't forget about #1 above; inserting a cartridge will cause the Mac to access SCSI, so don't try to use the K2K at that moment.

After experimenting we have discovered that when using a K2000 with a Mac and a K2000 formatted removable media drive in the middle of the chain, the following scenario will work:

Start with a Mac formatted cartridge in the drive. When you want to use the K2000, put the drive to sleep from the K2000. You can then change to a K2000 formatted cartridge and perform whatever disk operations you need. When you want to go back to the Mac, put the drive to sleep again, switch cartridges, and then wake up the disk by pressing Load. Of course the K2000 will tell you it can't read the cart, but the Mac will now access it fine.

Accessing a K2000 Internal Drive from the Mac

Access PC is one of the many programs for the Mac which allow it to format, read, and write to DOS floppy disks and removable SCSI cartridges. However, we have discovered that it is possible to format internal K2000 hard drives, even though the documentation claims to only support removable media (not a fixed drive). We tried this with v3.0, but other versions may also work. Because the program claims not to be able to do this, we do not necessarily recommend it. You will need the Media Formatter program, which comes with Access PC, to initially format the disk.

Some Final Points:

Never change the disk contents (i.e. save or delete files) from the K2000 and then try and access the disk from the Macintosh. If you do, this could easily lead to trashed files, directories, or even the entire disk. The Mac has no way of knowing when the K2000 has modified the disk structure, and it can just overwrite any state of the disk it thinks should be there. For removable media drives, the safest thing is to eject the disk, then reinsert it. This will cause the Mac to read the directory, getting an accurate description of the current state of the disk.

A similar situation can happen with the PC. Windows and possibly other 3rd party programs for the PC can set up caches for the disk, and they will not know if the K2000 has modified the disk. These caches should be disabled when using a K2000 in the PC's SCSI chain.