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mehguy

SCSI Interface question

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I have an Amiga 2500, and I want to be able to put perhaps a zip disk or a cd rom drive into it but its occupied with a HDD already. I have a A2091 SCSI controller and I'm not very familiar with SCSI. The SCSI ribbon cable doesn't have multiple connectors on it like a floppy or IDE ribbon cable has on it. Does this only support one device or do I need to purchase a SCSI ribbon cable with multiple connectors on it?

Edited by mehguy

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You'll need to read the documentation for your particular SCSI controller in order to know how it handles termination with multiple devices. For the most part, scsi can handle 7 devices from id 0 through 6 with 7 being its own id. And if you have the slots you can have multiple scsi controllers assigned to different LUNs.

Edited by Sinphaltimus

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All you need to know about termination http://computer.howstuffworks.com/scsi4.htm

 

Basically each drive will have a jumper on it to set/unset depending on if you want the termination to be active. Some devices have the resistors built in. Other devices need actual terminator packs plugged in to offer the resistance needed.

Edited by Arnuphis

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Be sure to read your card's documentation and how you want to set it up. For instance, gvp impact series II HD+, do not terminate anything internally as the board does that but if you want to add external also, you'll need to remove the internal terminators on the board and terminate the last device on the external chain.

 

As an example. Your card might have some caveats as well.

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What do you mean by "terminated"?

 

A nice way to think of device termination is to imagine bits flying though the cable. An un-terminated device would be like leaving an open water hose (the water would just run out the end). So if you had five devices in a row, you'd let the bits flow though until they hit the tail end of the last device (e.g. a hard drive). You'd terminate that last drive to keep data from spilling onto the floor.

 

Typically, you need to terminate the end of the chain internally and also the end of the external chain of devices. So that's one 'hose' running inside the computer's case and another one running outside of the case.

 

No need to terminate an unattached SCSI port on the SCSI card though.

 

The other detail is to make sure that everyone gets their own unique ID number (except for #7, since that's reserved for the SCSI card itself).

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