Alt-BEAM Archive
Message #12440
To: beam@sgiblab.sgi.com
From: Bruce Robinson Bruce_Robinson@telus.net
Date: Fri, 24 Mar 2000 18:47:51 +0800
Subject: Re: ....yet again.....
> "Scolman,Jim" wrote:
> >
> > ... in the enclosed diagram, one of the power leads goes to the
> > (+ plus) sign, where does the other go? ... where is the (- neg)
> > symbol?
>
> On the '240 chip, pin 10 is negative, or ground (Wilf used a little
> downward pointing triangle). Pin 1 (labelled 1G) and Pin 19 (labelled
> 2G) are the two "enable" pins are connected to ground as well; this
> basically turns the two halves of the chip "on".
>
> > Is this a Bicore, MicroCore, or UniCore?
>
> Microcore. This is typical Wilf :) The microcore couldn't be built on a
> '240 chip, it needed a Schmitt inverters; then Wilf came up with this
> circuit to prove the experts wrong. Here's his quote from the original
> message that accompanied this circuit:
>
> "Here is a tested 74HC240 microcore (no not a bicore)
> circuit which behaves just like a 74HC14 type microcore
> and motor driver combined."
>
> > ... All the "stuff" inside the outline of the chip ... is that internal
> > to the chip or are those parts and connections to be fabricated and
> > soldered?
>
> The inverters (large triangles with a dot on the pointy end, labelled
> "1" and "2") are internal to the chip. The four capacitors labelled C1
> (three drawn inside the chip outline, one outside) are external
> components.
>
> > ... I still don't understand about ground ...
>
> Just another way of refering to the negative connection of your power
> supply. I has it's roots way back in the days of vacuum tubes.
>
> > ... where do you connect the 1G and 2G pins? The R1 resitors that
> > just end in an arrow head......where do they connect?
>
> Those little down arrows are just a symbol for "ground", or the negative
> connection of your power supply.
>
> > I am electronically challenged ...
>
> We're all on the learning curve, just at different places. There's
> always someone a little higher up the curve :)
>
> A tip to help figure out the GND (negative) connection is this. On most
> of the 74-series chips (everyone I've ever encountered so far), the two
> power supplies are diagonally opposite. Positive is the highest numbered
> pin (directly across from pin 1), and negative is in the opposite row of
> pins, at the other end of the chip. If a person is using a symbol for
> GND that you aren't familiar with, identifying the ground pin this way
> helps you figure out what symbol is being used.
>
> Bruce
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