you need a centronics 50 pin (telco, but with bails instead of screw holddowns) and you should probably have active terminators on the infeed side of each for when the either computer is not connected to the terminated burner. you're looking at a pretty penny in price between the terminators and a switchbox. if a crossover switchbox is available you could try that with one standard terminator on the back end.

i've never tried it, but a DB25 crossover switchbox should work just as well, i never thought of using a crossover box to get around the termination problems before tonight. i used the centronics 50 switchbox on an electronics project and i have used it as a cutout to hot swap SCSI deviced (unpowered) so i didn't have to shut down my mac at times so termination was not an issue. i have two active terminators from old APS drives for the day that i get a decent PC in the shop again.

jt

=8-}

i have Quickshare, which i could explain in the peripherals forum if anyone is really interested. it makes a two machine network with an ISA card in a PC as SCSI 6 at the end of the mac's chain. the software sets up a virtual disk for the mac on the PC's HDD and allows file transfers at SCSI speeds, but the PC can't use it as a controller. it never made it to System 7, but i'll set it up again someday.

jt

technically, it's not good to have SCSI devices that have the same address on the chain even when only one is powered atany given time. i can't imagine having two bus masters in the same config is any better an idea.

jt

Been there done that with an external scsi hard disk and 2 amigas with scsi...

It ended up trashing one of the amigas internal scsi drives. oops. prolly because the host ID of the computer was the same, was unchangeable, and confused things :D.

AFAIK the host ID of a mac is always either seven or zero (I never remember which!) and with 2 ID's the same on a scsi chain thats all for causing confusion when they're both on!.

But what ~Coxy just said may work just fine, especially since external termination on most macs I've used is something you don't always need - and the mac-thats-not-turned-on may even supply termination as a side effect... if it is unpowered internal termination... thats a hardware level side of things I really couldn't do any more than guess at.

Of course, accidentally turning one mac on while the other is also could screw up the drive on one or both - but hey, thats all part of the fun!.

dana

i always understood it to be the case that one off at all times would be ok for the duplicate id thing, but very recently i read something i thought was trustworthy that said it was definitely NOT a good idea and could lead to dire consequences. dunno!

jt

I got a DB-25 A-a/B-b crossover to A-b/B-a switchbox and a 25 pin passive terminator that screws down like any DB-25 cable from these guys at a computer show today. connect a similar box and terminator as such:

7200--------------A-box-a----------------Terminator-External CD
840A/V------------B-box-b-Terminator

it changes with a flip of the switch (everything powered down to be safe, but it probably would be ok to hot switch WITH LUCK! and a devil may care attitude!) to this config:

7200--------------A-box-b-Terminator
840A/V-----------B-box-a----------------Terminator-External CD

no cable changes, no muss, no fuss, no fried SCSI controller IC's!

the crossover box is not listed, but they do exist!
the box is marked 25/X in magic marker on the bottom.

DB-25 ABXXXXX Switch Boxes:
http://www.cablesonline.net/dbparswitbox.html

Here is something that will be very handy, i got a few, the four way is in use at the moment, works great:

These Switch Boxes are used for sharing MAC Monitors or PC Joysticks:
http://www.cablesonline.net/dbmacorjoysw.html

They also have SCSI switchboxes (Centronics 50):
http://www.cablesonline.net/scsiswitbox.html

haven't tried the DB-25 SCSI switch box yet, but i can't see any reason for it to cause any problems at all!

have fun!
jt ™

which desktops have you heard about?

jt ™

jt ™