On Thursday, April 22, 2004, at 11:22 AM, Byron Q. Desnoyers Winmill wrote:
On Thu, Apr 22, 2004 at 11:11:40AM +0800, John Niven wrote:1) If you want to use the second bus to connect to a second internal drive, should that drive be terminated, and if so, does that mean you cannot connect an external SCSI device? My idea was to set up a second HD as a mirror.
Termination rules are the same, regardless of the number of busses you have: both ends of each bus must be terminated.
Yes, I understand but doesn't that mean that the motherboard already has a terminator built in? So if I used an internal (terminated) drive, and an external (terminated) chain, I would have:
Term <-> drive <-> Term (MB) <-> drive <-> Term
Is that OK?
2) I added a CDROM drive. Do Apple CDROMs act as terminators? I see
that there is a jumper that says "Termination Power". Does this control
the CDROM terminator (switch it on or off) or just whether it supplies
the busses termination power or not?
Termination power doesn't terminate the bus. If I recall correctly, it provides power for an active terminator. In general, only one device on each bus should provide termination power, but it doesn't matter which device. Some devices may have a termination switch, but most older drives will have resistor packets.
I've always assumed that the MB provided the termination power. In which case the CDROM termination power should be off. So I still need to know if the Apple CDROM acts as a terminator, or if I have to add a terminator to the cable.
John
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