By SimonInAustralia
Sun Dec 09, 2012 5:42 pm
MPCHunter wrote:SCSI devices do not know if they are internal or external. They only know that they are a SCSI device.
...and they only know how to talk to the SCSI controller over a transmission line that is configured in a particular and exact way.
If you setup that transmission line differently, outside of the specs, there is no way of knowing whether it will work correctly in various situations.
If you change the properties of that transmission line, making a "stub" off of the main SCSI bus that is longer than 10cms as the specs describe, it is possible that it can no longer communicate correctly, and it is unknown how it will react to various different external SCSI cabling configurations that would normally be within the SCSI specs.
MPCHunter wrote:Going back to the original topic of the thread, I think it's been clearly demonstrated here that a clever cabling solution is much more practical than redesigning the SCSI PCB.
If you don't like slop in your cables and having to use lots of adapters, you will have to have a custom cable built. You can certainly go over the maximum length spec if you can find cables that have a better attenuation spec.
Practical doesn't mean much to me, I will do something like this to make what I believe is a better/cleaner end solution, that I am happier with, no matter whether it seems practical to anyone else or not.
Along with much neater internal cabling, you could incorporate the SCSI termination for the external bus onto the new PCB, making it an even cleaner solution.
The cabling solution being used in the photos above is not clever, it is ugly and wrong, lazy and quite the opposite of clever in my opinion.
Back to the original topic of the thread, if I was going to go to the trouble of making a redesigned SCSI Jack PCB, I would do it properly, to give a correctly speced external SCSI chain, so that anyone using it can expect it to behave in a certain way, like an external SCSI chain should.
If you redesign the SCSI Jack PCB, there is no need for any custom cables or excessive use of adapters, you can simply use an off the shelf 50 pin internal SCSI ribbon cable, the way it should be.
Making an external SCSI solution that does not behave the way SCSI is supposed to, that only allows a single and unterminated device to be connected to the external SCSI port, outside the SCSI specs, as you are suggesting, would be a very strange way to do it.
If you provide a solution to be used by others, it needs to meet accepted standard specs, so it behaves as expected in the widest variety of circumstances.
I don't see what the problem is anyway, I have shown above that the same solution and parts can be reconfigured to give a SCSI bus that correctly meets the specified configuration.
I don't understand the insistence to set it up incorrectly, all it requires is an external SCSI terminator plug in addition to the parts above, for when there is no external SCSI device attached.
This thread is about possibly creating a cleaner and more correct solution, as shown above there are plenty of threads showing how to do it with adapters (incorrectly), why do you have a problem with some people wanting to do it in a different way, that they believe is neater/cleaner/better?
