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Re: [OCLUG-Tech] Re: Some questions about Intel use of transistors and logic gates ??

  • Subject: Re: [OCLUG-Tech] Re: Some questions about Intel use of transistors and logic gates ??
  • From: Charles MacDonald <cmacd [ at ] telecomottawa [ dot ] net>
  • Date: Sat, 01 Oct 2005 20:13:16 -0400
William Case wrote:
> Hi;

I agree we are getting somewhat (or more) off  the topic of the "on
topic list ...

William could you ask you question on the "main List"? where this is
closer than SOME of the recent topics.

> 1) a bit equals 1 or 0.  More concretely, 1 is a pulse made up of 5+
> volts while 0 is really a pulse made up of approximately 3 volts.

> In any case, is the above a fair description of what a bit is? 

Totally depends on the definition of the logic family you are using, The
newer processors are using smaller voltages all the time, so they have
the levels closer together.

If you were using Silicon Bipolar transistors the threshold for a PN
junction to conduct was 0.7 Volts.  So that is probably a good place to
set the difference from a 0 to a one in silicon based Logic. when the
book you are using was written TTL was in vogue.  It used a 5V supply,
and "close to 5v" was one and less than 2 and a bit volts was zero.
Before that their was "RTL Logic" which used very different levels.

Google for TTL Logic, and 4000 CMOS

One promising link from my search  looks like

Logic Voltage Thresholds for TTL, CMOS, LVCMOS, and GTLP IC's
Switching Levels, Chart of voltage thresholds for TTL,CMOS, LVCMOS, GTL,
BTL,
ETL, and BiCMOS devices. Includes a table showing prefix and
discriptions of ...
www.interfacebus.com/voltage_threshold.html - 15k - Cached - Similar pages

>  By using varying doping levels and varying voltage levels
> in a single transistor couldn't a trinary or a quadrinary, or a decimal
> computer system be built.  Putting aside why you might want to do that,
> is there any physical restriction on why it can't be done.?

Sure but them you logic gets scary, and you ability to separate noise
from signal goes way down.


> Lastly, as I look at various schematics of how a transistor works they
> all seem to show that when there is a 0 bit the current, of course, is
> too low of a voltage to complete the circuit.  Those same schematics
> show the low voltage being drained off to ground.  Why isn't the low
> voltage current used to form a separate low voltage path (circuit) so
> that a transistor would be 'either', 'or' rather than 'on', 'off'.

I am not sure what you are asking, the "other side" of the circuit is
normally "ground".  I think you are trying to have the transistor to
have more states, and again that would only complicate the logic, as you
would need MORE transistors, (or tubes, most of these logic ideas came
from the time when Special 6sn7, and 12at7 Tubes were the logic
ampliphiers.)

I have recent snagged a copy of the GE Glow lamp Manual, where they did
and and or gates  and even adders using neon bulbs. which have two
states, above 65 volts where they start to glow and below 55 Volts were
the go out.  if you keep them at 60 volts they will be in a state that
depends on the last pulse you fed them..  (Eureka - Computer memory)

Unless you want to design a computer from Scratch using discrete
transistors (or Tubes or neon Lights)  you should not try to worry about
the electrons flowing, and if you do, then you have to worry about
capacitance, inductance and the length of your signal part, (LOok up
Admiral Grace Hopper and her "nanosecond Wire"


-- 
Charles MacDonald      cmacd [ at ] TelecomOttawa [ dot ] net     Stittsville Ontario
1800+ Canadians oppose Bill C-60 which protects antiquated Recording,
 Motion Picture and "software manufacturing" industries from change...
                   http://www.killbillc60.ca