jjs@PRC.Unisys.COM (James Solderitsch) (07/31/89)
I have spent a frustrating day trying to add a 45 meg cartridge drive
to my Mac Plus system (2.5 megs, system 6.02) that already was using
and FX-20 (GCC 20 meg SCSI drive). I thought I knew how to do it -- it
should be trivial, right? Maybe some of you with multiple read/write
SCSI devices on the SCSI port have walked this road before.
I bought the SyQuest drive used and it came with no manual and has
no brand name on the case. It has the usual black SyQuest drive casing
in the front, two DB-25 style female connectors on the rear as SCSI in/outs,
a terminator switch and a SCSI priority selector switch.
I have tried various combinations of device positioning (which drive is
first on the chain) and terminator locations. I have settled on the
following for now: FX-20 (boot device, priority 6) first, cartridge
drive second (priority < 6), no terminators on the FX-20, terminator switch ON
on the cart. drive. This works mostly ok except I can't run the
FX-20 by itself with the cartridge drive off. I can boot from the
FX-20, and both devices come on-line -- there seems to be some
intermittant hesitation at start-up until the boot process begins.
Interestingly, if I add a terminator on the incoming SCSI port on the FX-20,
I can run the FX-20 stand-alone. I can run the cartridge
drive with the FX-20 off, either as a data disk (booting from
a floppy) or booting from a system-equipped cartridge, as long as there
is no terminator installed on the FX-20. If I put in that terminator
to let the FX-20 run by itself, I can no longer use the cartridge drive
as a data drive when booting from a floppy (with the FX-20 OFF)
-- it never comes on line.
I would like to do this for the sake of older software like games
that don't run correctly when invoked under 6.02.
What I want
is to run with either of the devices on, separately or together, or off.
I can't seem to achieve this.
Let me ask a couple of specific questions.
1. Must (should?) all SCSI devices on the chain be powered up when
the system is running. I had assumed this was false, now I am not so
sure. Can devices on the chain be selectively powered up in general?
2. What is the current practice for installing SCSI terminators? I had
assumed 1 was sufficient, but after my experiences I am not so sure.
My FX-20 manual and a recent article in MacWorld say a SCSI chain containing
2 or more devices should be bracketed by 2 terminators: one at the
beginning and one at the end of the chain. This arrangement precludes
using the second device on the chain stand-alone (with the first one
powered off) which I would like to do.
I don't recall this issue being discussed on the net recently, so replies
by mail or to the net encouraged.
Thanks
Jim Solderitsch
USENET: sdcrdcf!burdvax!jjs
{sdcrdcf,bpa,psuvax1}!burdvax!jjs
ARPANET: jjs@burdvax.prc.unisys.comkaufman@polya.Stanford.EDU (Marc T. Kaufman) (08/01/89)
In article <11004@burdvax.PRC.Unisys.COM> jjs@PRC.Unisys.COM (James Solderitsch) writes: >I have spent a frustrating day trying to add a 45 meg cartridge drive >to my Mac Plus system (2.5 megs, system 6.02) that already was using >and FX-20 (GCC 20 meg SCSI drive). I thought I knew how to do it -- it >should be trivial, right? Maybe some of you with multiple read/write >SCSI devices on the SCSI port have walked this road before. The Mac Plus does not provide terminator power on the SCSI connector, and most devices that have internal terminators, cannot power the terminators from outside the unit. If ANY device has terminators on (in) it, they must be powered up for the bus to operate (otherwise they look like 135 ohms to ground, which keeps the bus from sending any signals). You have two choices: NO terminators at all, which usually works with short cable runs, or a terminator on the far-end device, which (usually) must be powered by that device -- which means the device must be turned on. >I have tried various combinations of device positioning (which drive is >first on the chain) and terminator locations. I have settled on the >following for now: FX-20 (boot device, priority 6) first, cartridge >drive second (priority < 6), no terminators on the FX-20, terminator switch ON >on the cart. drive. This works mostly ok except I can't run the >FX-20 by itself with the cartridge drive off. Right, since the cartridge drive provides power to the terminators within it, but those terminators can't be powered by the FX-20 (even if it puts power out on the bus, which is probable, given your other configuration). >If I put in that terminator >to let the FX-20 run by itself, I can no longer use the cartridge drive >as a data drive when booting from a floppy (with the FX-20 OFF) because the FX-20 is not powering the terminator, and neither is the cart. drive. >What I want >is to run with either of the devices on, separately or together, or off. Try NO terminators, and short cables. good luck. Marc Kaufman (kaufman@polya.stanford.edu)