Vladimir Vassilevsky wrote:

> 
> 
> rickman wrote:
> 
>>
>> I understand what you are saying, but your first few posts were not at
>> all clear and only appeared to be attacks on others.
> 
> 
> I have to admit that I didn't expect the cross conduction to be that 
> high in the HCT at 3.3V input levels. Actually it made me rethink my 
> position. The HCTs can be used as 3.3V -> 5V level translators, however 
> the user must be aware of the power consumption.
> 
> BTW, the maximum of cross conduction appears to be at 0.9V input (5Vdd), 
> and it is about 4mA.

It's generally quite poorly documented, and varies across vendors,
and Logic families. The Schmitt devices tend to have lower peaks than
non schmitt devices.
Seems to be an after-thought to most digital designers....

-jg

On Tue, 28 Nov 2006 17:48:19 GMT, Vladimir Vassilevsky
<antispam_bogus@hotmail.com> wrote:

>
>
>rickman wrote:
>
>> 
>> I understand what you are saying, but your first few posts were not at
>> all clear and only appeared to be attacks on others.
>
>I have to admit that I didn't expect the cross conduction to be that 
>high in the HCT at 3.3V input levels. Actually it made me rethink my 
>position. The HCTs can be used as 3.3V -> 5V level translators, however 
>the user must be aware of the power consumption.
>
>BTW, the maximum of cross conduction appears to be at 0.9V input (5Vdd), 
>and it is about 4mA.
>
>VLV

Theoretically it should be maximum at the design center of the TTL
threshold, ~1.4V.

Maybe the 0.9V you measure is just process skew?

                                        ...Jim Thompson
-- 
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

rickman wrote:

> 
> I understand what you are saying, but your first few posts were not at
> all clear and only appeared to be attacks on others.

I have to admit that I didn't expect the cross conduction to be that 
high in the HCT at 3.3V input levels. Actually it made me rethink my 
position. The HCTs can be used as 3.3V -> 5V level translators, however 
the user must be aware of the power consumption.

BTW, the maximum of cross conduction appears to be at 0.9V input (5Vdd), 
and it is about 4mA.

VLV

On 27 Nov 2006 11:09:33 -0800, "rickman" <gnuarm@gmail.com> wrote:

>Jim Thompson wrote:
>> "HCT" parts were designed to receive signals from TTL parts also
>> operating at VDD=5V.
>>
>> The shifted threshold was done to minimize timing skew when making the
>> translation.
>>
>> Over time they've come to be misused as logic level translators, even
>> though there are specific parts for such purposes.
>>
>> Unfortunately many lurkers here presume that "getting away with it" is
>> good engineering practice :-(
>>
>> Me, I have to deliver good stuff every time... otherwise I'm
>> unemployed.
>
>I understand what you are saying, but your first few posts were not at
>all clear and only appeared to be attacks on others.  I am not trying
>to place any blame for this flame war, as there is plenty of blame to
>go around.  I would suggest that you might consider how your posts
>appear to a third party reading this.  Take it from someone who knows,
>this is not the best way to promote yourself.
>
>BTW, sort of like in the movie Chinatown, "Let it go Jack, it's just
>the Internet!"

One of my favorite movies... in my DVD collection ;-)

You're right, I should ignore the flack.

                                        ...Jim Thompson
-- 
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Mike Monett wrote:
> "rickman" <gnuarm@gmail.com> wrote:
>
> > Maybe I don't undestand what you mean by "copperclad".  To me that is
> > the same as PCB.  Are you talking about mouting components to a
> > pre-etched general prototype board or a PCB that has *not* been etched
> > at all, or something else?
>
> Bare copper on fr4. You can usually get scraps from any pcb house for free.
> Only one side needs copper. You can cut it with a knife, hacksaw or tin
> snips to the required size.

Ok, this is not addressing my question.  I know what copperclad is.  I
don't understand how you are using it.


> There are many ways of mounting the components. I use plain hot glue most
> of the time, but also screw components such as heatsinks to the board if
> needed. You can cut the plane to isolate components if needed.

Are you saying that you are just using the board as a mechanical mount
and not to make connections?  How do you make connections with point to
point wires?


> See Terry Ritter's page for an example of Manhattan style:
>
>   http://www.ciphersbyritter.com/RADELECT/BREADBD/BREADBD.HTM

Ok, I guess this is a bit more clear.

> Since the copper is not cut or etched, it makes a much better ground plane
> than a pcb, and you can get excellent analog and digital performance up to
> about 1GHz. However, fast risetimes do not do well with copper wire
> interconnections. For example, the Motorola EclInPs with 160ps risetime is
> a problem. You really need stripline or microstrip to handle these signals.
>
> A big advantage is you can easily move parts around if needed to add new
> circuitry. But complex circuits with a wide data buss would be difficult
> to wire.
>
> After a few days, you will see your fingerprints etched into the surface.
> The copper may eventually darken due to corrosion. Brasso may clean the
> oxides off, but I'd rinse the board carefully to remove any trace of acids.
>
> The technique is ideal for testing new components or circuit concepts.
> People have made entire high-performance radio receivers using this method.
> Each circuit sits in its own shielded box for good isolation. When you want
> to try a different mixer or amplifier, it's easy to pop a new board in and
> test it under actual conditions.

This seems very difficult to me, but I do digital much more than analog
and the number of connections with multi-pin packages is much higher.

Jim Thompson wrote:
> "HCT" parts were designed to receive signals from TTL parts also
> operating at VDD=5V.
>
> The shifted threshold was done to minimize timing skew when making the
> translation.
>
> Over time they've come to be misused as logic level translators, even
> though there are specific parts for such purposes.
>
> Unfortunately many lurkers here presume that "getting away with it" is
> good engineering practice :-(
>
> Me, I have to deliver good stuff every time... otherwise I'm
> unemployed.

I understand what you are saying, but your first few posts were not at
all clear and only appeared to be attacks on others.  I am not trying
to place any blame for this flame war, as there is plenty of blame to
go around.  I would suggest that you might consider how your posts
appear to a third party reading this.  Take it from someone who knows,
this is not the best way to promote yourself.

BTW, sort of like in the movie Chinatown, "Let it go Jack, it's just
the Internet!"

> > The reason why I believed that a 3.3v '1' would register as a '1' on a CMOS
> > dsPIC port is that there are quite a few examples on the net that say it
> > works...  That was my mistake, believing what I read on the Internet.
>
> isn't High typically specced as anything above 2/3 VCC.... (that'd be 3.33v)

Three things:

a)  Vih is typically 0.7*VCC (that'd be 3.5V).  Minor difference, but
see..

b)  A 3.3V <> 5V circuit contains two power supplies, each with its own
tolerance.  If 5V goes +5% (5.25V) and 3.3V goes -5% (3.135V) at the
same time, the situation gets worse.  Vih is now 0.7*5.25V = 3.675V,
while the 3.3V sender can generate 3.135V max.

c)  You're missing that a 1 generated by a 3.3V device is not 3.3V.
It's Voh.  Typically CMOS outputs tend to climb up to almost VCC, but
not all do.  And certainly some devices trade lower Voh for a faster
timing spec (ie faster device without silicon change).

A fool who thinks that this might be related to the timing problems of
the GP... ?!

Regards,
Marc

"rickman" <gnuarm@gmail.com> wrote:

> Maybe I don't undestand what you mean by "copperclad".  To me that is
> the same as PCB.  Are you talking about mouting components to a
> pre-etched general prototype board or a PCB that has *not* been etched
> at all, or something else?

Bare copper on fr4. You can usually get scraps from any pcb house for free. 
Only one side needs copper. You can cut it with a knife, hacksaw or tin 
snips to the required size.

There are many ways of mounting the components. I use plain hot glue most 
of the time, but also screw components such as heatsinks to the board if 
needed. You can cut the plane to isolate components if needed.

See Terry Ritter's page for an example of Manhattan style:

  http://www.ciphersbyritter.com/RADELECT/BREADBD/BREADBD.HTM

Since the copper is not cut or etched, it makes a much better ground plane 
than a pcb, and you can get excellent analog and digital performance up to 
about 1GHz. However, fast risetimes do not do well with copper wire 
interconnections. For example, the Motorola EclInPs with 160ps risetime is 
a problem. You really need stripline or microstrip to handle these signals.

A big advantage is you can easily move parts around if needed to add new 
circuitry. But complex circuits with a wide data buss would be difficult 
to wire.

After a few days, you will see your fingerprints etched into the surface. 
The copper may eventually darken due to corrosion. Brasso may clean the 
oxides off, but I'd rinse the board carefully to remove any trace of acids.

The technique is ideal for testing new components or circuit concepts. 
People have made entire high-performance radio receivers using this method. 
Each circuit sits in its own shielded box for good isolation. When you want 
to try a different mixer or amplifier, it's easy to pop a new board in and 
test it under actual conditions.

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
 http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
 http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
 http://www3.sympatico.ca/add.automation/sampler/intro.htm

Jim Thompson wrote:
> On Sun, 26 Nov 2006 18:00:38 -0500, Mike Monett <No@email.adr> wrote:
> 
> [snip]
>>  Figure 7. Supply Current as a Function of the Input Voltage
>>
> [snip]
>>  http://focus.ti.com/lit/an/scla011/scla011.pdf

> If 'HCT04 were a good general solution to 3.3V to 5V translators,
> wonder why they make true translator chips like the Maxim MX3xxxx to
> name just one?  For their health?  I doubt it.

RTFM and think. Give it a try.

HCT/AHCT is good only for unidirectional 3.3V->5V translation. In this 
case it is the most convenient and least expensive solution.

Specialized IC can be used for bidirectional level translation, when 
different voltage levels required, like 1.8 <-> 3.3V, etc.

-- 
WBR, Yuriy.
"Resistance is futile"