What "Parallel Hz" Really Is

[Keith]

Your design? Everything leaks, make more of 'em and they leak more.
You've added a billion more leakers. You can look at David Wang's
excellent "garden hose" analogy in this thread
comp.sys.ibm.pc.hardware.chips.

Okay. I read it. I understand leaking a bit more. I understand that
using 4 billion 1 hz clocks to gain a clock rate of 4 Ghz would leak
[well, any electronic mechanism "leaks" to some extent]. What I don't
understand is why would it leak 3999999999/4000000000ths of the time?

Each one of your clocks is doing nothing for 3999999999/4000000000ths of
the time. Whether it is doing anything or not, it's leaking. Since it's
not doing anything, it's not producing anything for that time. Of course
1/4000000000ths of the time that clock circuit is doing something useful.
Now, wouldn't it be nice to up the percentage of useful time?

 

[Del Cecchi]

I didn't think so because the output current was limited to
~B(3.6/Rc2). With a darlington there wouldn't be much current
limiting (B^2 *3.6/Rc2).

They usually put a small resistor in series with the pull up device(s)
for short circuit protection. 40 ohms as I recall for S. But the bible
is at work.

 

[Rob Warnock]

+---------------
| Schottky clamped TTL has schottky diodes from base to collector
| on Q2 and Q4 (IIRC) to prevent saturation.
+---------------

The TI 54/74Sxx series [and competitors] also used Schottky
clamping on Q1 [the input transistor] as well -- yes, even
those with multiple-emitter inputs. They also used Schottkys
for the Darlington driver of the upper output stage [which
you didn't show -- it would have driven your Q3's base] and
for the anti-overdrive transistor [also not shown] clamped
on the base of Q4. In fact, of the six transistors in the
small 54/74Sxx series, only the one matching your Q3 was
*not* Schottky-clamped. ;-}


-Rob

 

[Rob Warnock]

+---------------
| (e-mail address removed) says...
| > Keith wrote:
| > >The input logic *TRANSISTOR* makes the 74xx series "Transistor-
| > >Transistor Logic". Replace the input transistors with *DIODES* and
| > >it becomes Diode-Transistor Logic, or DTL.
| >
| > The transistors were not replaced with diodes in S and LS logic.
| > S and LS is still TTL, schottky clamps and all.
|
| Please read what I've written again. You're simply wrong.
+---------------

Actually, he's exactly half-right! ;-} I just looked it up
in an old TI 54/74 Data Book. The 'S series still had true TTL
inputs (albeit Schotty-clamped), but the 'LS series had DTL inputs
(using Schotty diodes) feeding a Schotty-clamped phase-splitter.


-Rob

 

[chrisv]

(e-mail address removed) says...
Please read what I've written again. You're simply wrong.

I checked "the reference", and I was correct regarding S logic, but
incorrect regarding LS logic. The former has the emitter inputs, the
later has the diode inputs. So I guess it was a split decision. 8)

 

[Del Cecchi]

+---------------
| Schottky clamped TTL has schottky diodes from base to collector
| on Q2 and Q4 (IIRC) to prevent saturation.
+---------------

The TI 54/74Sxx series [and competitors] also used Schottky
clamping on Q1 [the input transistor] as well -- yes, even
those with multiple-emitter inputs. They also used Schottkys
for the Darlington driver of the upper output stage [which
you didn't show -- it would have driven your Q3's base] and
for the anti-overdrive transistor [also not shown] clamped
on the base of Q4. In fact, of the six transistors in the
small 54/74Sxx series, only the one matching your Q3 was
*not* Schottky-clamped. ;-}


-Rob

Adding the schottky diodes was easy. All you had to do was allow the
base contact to overlap the edge of the P diffusion onto the n-
collector(epi).

 

[Keith]

+---------------
| (e-mail address removed) says...
| > Keith wrote:
| > >The input logic *TRANSISTOR* makes the 74xx series "Transistor-
| > >Transistor Logic". Replace the input transistors with *DIODES* and
| > >it becomes Diode-Transistor Logic, or DTL.
| >
| > The transistors were not replaced with diodes in S and LS logic.
| > S and LS is still TTL, schottky clamps and all.
|
| Please read what I've written again. You're simply wrong.
+---------------

Actually, he's exactly half-right! ;-} I just looked it up
in an old TI 54/74 Data Book. The 'S series still had true TTL
inputs (albeit Schotty-clamped), but the 'LS series had DTL inputs
(using Schotty diodes) feeding a Schotty-clamped phase-splitter.

No, he's not. Go back and read the thread again (where the
transition was made has been discussed at length).

 

[Keith]

I checked "the reference", and I was correct regarding S logic, but
incorrect regarding LS logic. The former has the emitter inputs, the
later has the diode inputs. So I guess it was a split decision. 8)

NO, the drawing I included (up there somewhere) had the 74xx and
74Sxx clearly in the TTL category (though some S is DTL according
to one poster) and LS and newer in the DTL category.

<from somewhere up there>:

Circuit diagrams (note: from rusty memory)

TTL (74xx and 74Sxx): Vcc
^^^^^ |
.-.
Vcc | | Vcc
| | |
.-. '-' |
| | | |/
| | +---+-| Q3
'_' | |>
| | |
----- |/ V
A1 0----vv \-----| Q2 -
A1 o----/ Q1 |> +-------o O
| |/
+----+| Q4
| |>
.-. |
| | GND
| |
'-' created by Andy´s ASCII-Circuit
| v1.22.310103 Beta www.tech-chat.de
GND

Schottky clamped TTL has schottky diodes from base to collector on
Q2 and Q4 (IIRC) to prevent saturation.

SDTL (74LSxx, 74ASxx, 74ALSxx, etc.):
^^^^^^^^^^^^^^^^^^^^^^^


VCC VCC
| .-. VCC
.-. | |
| | | | |
| | '-' |/
'-' + -|
| | |>
| | |
A1 o-S<--+ |/ V
+--->S-----| -
A2 o-S<--+ |> +--- O
| |/
+--|
| |>
.-. |
| | GND
| |
'-'
|
GND

 

[Keith]

They usually put a small resistor in series with the pull up device(s)
for short circuit protection. 40 ohms as I recall for S. But the bible
is at work.

Yes, the darlington and curent limters are clear in the drawings
Spehro linked. I'd forgotten that piece.

(bottom two):

http://www.ee.washington.edu/stores/DataSheets/74ls/74ls00.pdf

 

[chrisv]

NO, the drawing I included (up there somewhere) had the 74xx and
74Sxx clearly in the TTL category (though some S is DTL according
to one poster) and LS and newer in the DTL category.

Okay, I missed that detail in your post. But that doesn't make my
statement above "simply wrong". Half of my assertions were correct.

 

[Keith]

Okay, I missed that detail in your post. But that doesn't make my
statement above "simply wrong". Half of my assertions were correct.

The sun rises in the East too but that wasn't be discussed either.

 

[chrisv]

The sun rises in the East too but that wasn't be discussed either.

"wasn't be discussed"? I don't know what that means. Of course, I
realize that communications errors will sometimes occur on both the
send and receive ends.

I believe that my comments were on-topic, if imperfect. Astronomical
events are not on-topic, and cannot be compared to any of my comments.

 

[Keith]

"wasn't be discussed"? I don't know what that means. Of course, I
realize that communications errors will sometimes occur on both the
send and receive ends.

Fingle-fumber with an over-edit thrown on for good measure. ;-\
Try: "The sun rises in the East too but that wasn't being discussed
either"

I believe that my comments were on-topic, if imperfect. Astronomical
events are not on-topic, and cannot be compared to any of my comments.

I never said that the schottky clamps somehow made TTL into DTL,
which was what you tried to force into my mouth by your editing and
response (hence my strong objections to your articles). My point
was always about the *LOGIC* part of the circuit rather than the
amplifier clamps being the key to TTL vs. DTL). You maintained
that it was *ALL* TTL, which it is clearly not and I called you on
that statement.

I said several times that the 74Sxx line was TTL, at least in the
beginning but couldn't remember exactly when/where the switch-over
took place. Others pointed out that the 74Sxx line wasn't all TTL
(complex functions are DTL) and the 74LSxx was (all DTL).