Re: Updated MaxSonar-EZ1 Datasheet and Updated Website

"Wayne C. Gramlich" <Gramlich@xxxxxxxxxxx> wrote in message
news:dzRCf.22799$F_3.8595@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> The *definition* of RS-232 is that a voltage less than -3 volts
> corresponds to a logical "1" and a voltage greater than 3 volts
> corresponds to a "0". The definition is not open to discussion.

Agreed. Added though, RS232A limited maximum excursions to +25 and -25
as well.RS232C limited maximum excursions to +15 and -15 as well.

But yes, I agree, fr RS-232, a -3V (to something depending on spec of
choice) is a logical "1".

> Since a MAX232 level converter takes 5V <=> -12V and 0V <=> 12V, it is
> technically a buffer, not an inverter.

I disagree. It is not a buffer, per sa. And I will even say it is not an
inverting buffer or a non-inverting buffer, both of which terms are
used. For proof I offer the 74HC240, which you will find is classified
as an octal Buffer / line driver; 3-state inverting.

http://www.semiconductors.philips.com/pip/74HC240.html

as opposed to say at 74HC244, which you will find is classified as an
octal buffer / line driver; 3-state (non-inverting).

http://www.semiconductors.philips.com/pip/74HC240.html

A MAX232 is a level shifter. And I would also argue it is an inverting
level shifter. I do so based on manufacturer's data sheets.

> RS232 communication is *not* inverted. A "1" in your data is
> represented as a correct RS-232 "1" (i.e. -12V)

While I can see your point, something with a logical 1 where it should
be might not be inverted, I think you are focusing on final
interpretation of the signal, and ignoring the view point of the driver
which has no preset knowlege of what is a 0 or a 1 and only does the
level shifting. Well, we could get into relativity theory, because
something cannot be inverted by itself, but must be inverted relative to
something else. Therefore RS-232 is not inverted compared to RS-232. It
is however inverted compared to TTL synchronous serial, and vice versa.

> The bubble does indeed mean inversion and I would argue that placement
> of the bubble in the spec. sheet is in fact incorrect. Mind you, I am
> a hypocrite on this topic, since all my schematics that use the MAX232
> have the bubbles in them.

I think the bubble is correct, and possibly this argument might change
your position and "hypocracy" back to orthodoxy.

> Let me reiterate, as far as I am concerned, the MAX232 buffer is in
> fact a valid voltage level shifter that does not invert the data as
> it goes through.

Here's looking into the link to the MAX drivers of the last post.
http://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf
RS-232 Drivers

The typical driver output voltage swing is ±8V whenloaded with a nominal
5k? RS-232 receiver and VCC = +5V. Output swing is guaranteed to meet
the EIA/TIA-232E and V.28 specification, which calls for ±5V minimum
driver output levels under worst-case conditions. These include a
minimum 3k? load, VCC = +4.5V, and maximum operating temperature.
Unloaded driver output voltage ranges from (V+ -1.3V) to (V- +0.5V).

Input thresholds are both TTL and CMOS compatible. The inputs of unused
drivers can be left unconnected since 400k? input pull-up resistors to
VCC are built in (except for the MAX220). The pull-up resistors force
the outputs of unused drivers low because all drivers invert.

Now what about the receivers.

RS-232 Receivers

EIA/TIA-232E and V.28 specifications define a voltage level greater than
3V as a logic 0, so all receivers invert.

I think it is important to remember it would be possible to make a
non-inverting chip that shifted to the same (if opposite) levels. I
don't know of any, but it would be possible. So the one made for RS-232
conversion is the inverting one (electrically, not logically), and
should remain being called one, just as the manufacturer does, and the
schematics show (bubble on output).

--
Randy M. Dumse

Caution: Objects in mirror are more confused than they appear.


.

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