SCSI Termination and ID

Q) Once and FOR ALL, how must I terminate my devices on a SCSI chain?
Q) Is my AKAI Terminated ( the SCSI terminology:)?
Q) If I have INTERNAL and EXTERNAL SCSI devices attached to my Host Adaptor,what devices should I terminate?
Q) How can I remove/disable or insert/enable these terminators?
Q) What is an ID and how can I change it?
Q) What are the basic points of SCSI termination and IDing?

A) This is a delicate and crucial argument that stands right in the heart of a stable scsi chain. I have seen many people connecting/disconnecting, moving and rearranging devices in the same SCSI chain or from one chain to another without even bothering to check the terminations just as if they didn't even exist! Ofcourse this always lead to device malfunction or even failure at some point of the day and that's when I come in:) Actually it is not so difficult once you have got the message, so here we go: the first and last devices in a scsi chain are the devices that are at the TWO EXTREMES of the scsi cable. In this way if you have a PC-ZIP-AKAI chain the PC's host adaptor is the first or last device and the AKAI is the last or first device. The zip is in between thus must *NOT* be terminated. In the other case, if we have an INTERNAL ZIP-SCSI ADAPTER-AKAI then the first and last devices are the ZIP and the AKAI. People tend to "forget" that the scsi host adaptor IS a scsi device with it's own scsi ID and so do not consider it in an internal and external chain leaving the terminators on it. Infact if any of you have a SCSI adaptor with a BIOS scan, you will notice that by default the ID:7 is ALWAYS assigned to the SCSI HOST adaptor as if it where like any other scsi device along the chain. Fortunately some of these models have a function "AUTO TERMINATION" which automatically removes the terminators (electronically ofcourse) when there is an internal to external bus detected (like on the more expensive 2940A model). Please bare in mind that your AKAI is like any SCSI device - or better HOST ADAPTER - and if it is at the end/beginning of a chain it must be terminated; by your luck it already IS by default, whether it is turned ON or OFF. And you may have noticed another thing: having only one SCSI DB25 connector on the back, it cannot be connected in between a chain, unless one buys an appropriate scsi "doubler" cable (if for example you have to insert TWO AKAI samplers in a SCSI chain WITH your PC - but let's not get messed up;).

    Now that you know which devices must be terminated and which not, you have got to "proceed" in checking and setting their terminations and while you're at it you can check their individual IDs too. This can be easy if one has just a ZIP drive in a SCSI chain with your AKAI and PC because all you will have to do is DISABLE the termination switch on the back of the ZIP knowing that the AKAI and the PC's SCSI controller are by default already terminated. On the contrary, it can get challenging when one has more devices in his chain like having an INTERNAL SCSI CD-ROM, an INTERNAL ZIP DRIVE and an external HD with at the end of your chain your AKAI sampler. In this case the first device will be your internal SCSI CD-ROM drive so this should be terminated. This is usually quite easily done by inserting a jumper on the back of the drive in the appropriate position marked by the label "term"; if you are in doubt just consult the documentation of the device. Next is the internal ZIP drive which musn't be terminated; again the same procedure applies but in this case the jumper should be removed; a good thing to do when fiddling with jumpers to not loose them, is to insert the jumper on only one pin so that it actually doesn't "jumper" anything but stays there for future variations. Now comes your Host Adaptor. Well if it has the autotermination feature, then just don't do anything at all because it will automatically remove the termination at power up. If it doesn't you'll have to document yourself on how to disable/enable it's termination; usually, if it has onboard BIOS and a setup, enter it at boot by pressing the relative key combination and check the the options. There should be a "termination" voice somewhere in the setup menus. If you've checked and didn't find anything then maybe your controller doesn't have an electronic type of terminator but a "passive" one like a resistor series. You can easily check this out by looking at your adaptor card: you will notice THREE usually black "thingies" that are each 1mm think and around 25mm wide positioned in line one next to the other (like on the Adaptec 1505/10). These must all be removed if you have internal and external devices on your chain like in this case; so just pull them with decision from the center using your thumb and index finger and they will pop out from their socket. Done this, wrap them up with a piece of sellotape and stick them somewhere on your SCSI card or computer chassis out of trouble. So now to your external Hard Disk which mustn't be terminated being in the middle of a chain. If you have received it fully functioning already in a SCSI device container then you should've noticed on the back of it two CENTRONIC 50pin type connectors that resemble your printer's parallel port connector which is of the same type but shorter - I repeat the PRINTER type connector not the one on your computer which is a female DB25pin. Also, you should notice a little black push-pull switch which has a little window with a number in it which is the device ID - set it to a unique ID (remember NOT 7 or 6). Next, having localised the two centronics connectors, all you need to do is connect the cable from your SCSI card and the cable from your AKAI to the two connectors (it doesn't matter which one to which becuase the connectors are in parallel) assuming you have all the right cables with the right type of connectors on them. If instead you have bought a SCSI Hard Disk and the SCSI HD container seperately and you wish to mount it in the box yourself, check out the HD BOX MOUNTING procedure. That's about it; your SCSI chain should be checked and ready to go!

So to sinthesise the basic SCSI rules:

1) In a SCSI chain, the first and last devices *MUST* always be terminated.
2) The host adapter must be terminated if you have only external OR internal SCSI devices, becoming the end or beginning of the chain.
3) If one has internal AND external devices, thus using BOTH connectors on the SCSI adaptor, the termination on the controller MUST be removed due to the fact that the first and last devices have become the first internal device (at the END of the flat cable) and the last external device (at the end of the ext cable) which must be terminated.
4) All the devices on the same chain MUST have UNIQUE IDs.
5) The host adapter's default ID is 7 and shouldn't be changed.
6) The AKAI IS terminated by default whether it is powered ON or OFF.
7) The AKAI has by default ID:6 which should not conflict with any other device ID along the chain and should be left as is for compatibility and easier use (no need to re-set it at power on).