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On 5/26/2010 10:43 AM, Darren New wrote:
>
> They're not pull-down resistors at the end of the chain?
>
Just did a quick read on SCSI termination. Yes, they are pull down
resistors!
--
~Mike
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Mike Raiford wrote:
> On 5/26/2010 10:43 AM, Darren New wrote:
>
>>
>> They're not pull-down resistors at the end of the chain?
>>
>
> Just did a quick read on SCSI termination. Yes, they are pull down
> resistors!
I never looked it up specifically, but it's pretty obvious from looking at
the SCSI protocol specs that the addressing and bus mastering and such works
by pulling down zeros and letting ones float. Hence the "SCSI Priority"
being the LUN and having "0" always be the host. It's a pretty common way
of working a shared bus, from ISDN to those one-wire protocol capsules.
--
Darren New, San Diego CA, USA (PST)
Ada - the programming language trying to avoid
you literally shooting yourself in the foot.
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On 5/26/2010 5:16 PM, Darren New wrote:
> I never looked it up specifically, but it's pretty obvious from looking
> at the SCSI protocol specs that the addressing and bus mastering and
> such works by pulling down zeros and letting ones float. Hence the "SCSI
> Priority" being the LUN and having "0" always be the host. It's a pretty
> common way of working a shared bus, from ISDN to those one-wire protocol
> capsules.
Yep... Except often times when I think terminating resistor, I'm
thinking a resistor connected at the ends of the line to damp reflected
signals.
--
~Mike
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Mike Raiford wrote:
> Yep... Except often times when I think terminating resistor, I'm
> thinking a resistor connected at the ends of the line to damp reflected
> signals.
Given that SCSI allows cables up to 50' or something, I suspect they serve
both purposes.
--
Darren New, San Diego CA, USA (PST)
Ada - the programming language trying to avoid
you literally shooting yourself in the foot.
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Well let me see now... I bought a couple of switches and resistors, and
spent the morning soldering them together. I now have two switches - a
rocker switch and a push switch. In one position, you get logic 0, in
the other position, you get logic 1, and no floating inputs. Yay, me!
It's kind of frustrating how many problems I'm having with this whole
exercise - and most of them aren't electrical. They're mundane physical
issues. (E.g., one of the switches I bought has metal terminals with
small holes to poke the wires through. Except they're too tiny to poke
any wire through!)
Still, it was gratifying to flick some switches and watch an LED light,
correctly implementing the truth table of a NAND gate.
I was about to try rigging up a simple binary half adder - and then I
realised that this requires 7 NAND gates, and I obviously only have 4. >_<
I've bought a small plastic box, and I'm hoping to somehow mount some
switches on it, common-up the power rails, and end up with a box which I
can just connect to the power and have a nice set of output wires. But
this requires drilling and soldering and all sorts.
It's times like this where I miss my old electronics kit. :-( Everything
seemed so much easier back then...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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