Whats the purpose of Level Shifter (UART<->RS232C)

Iftikhar wrote:
Whats the purpose of Level Shifter.

MAX3232, etc...
Click to expand...
RS232 voltages are not the same as microcontroller voltages.

A PIC I/O pin might be 0v off, 5v on, where RS232 needs -5V on, to 5V
off (I think).

Al
 
Iftikhar wrote:
Whats the purpose of Level Shifter.

MAX3232, etc...
Click to expand...
Transmitting 0-5v over some distance is unreliable. RS232 (+/-15v, but
varies anywhere between +- 4-15v in practice) is more realiable over longer
distances up to about 20m reliably, possibly more under good conditions.

If you're using serial comms between two pieces of equipment that are in
close proximity, you wouldn't need to do any level conversion. Saves a bit of
cost for the interface electronics too.


--
Linux Registered User # 302622 &lt;http://counter.li.org&gt;
 
In article &lt;40aad995$0$16593$5a62ac22@freenews.iinet.net.au&gt;,
Al Borowski &lt;aj.borowski@erasethis.student.qut.edu.au&gt; wrote:
A PIC I/O pin might be 0v off, 5v on, where RS232 needs -5V on, to 5V
off (I think).
Click to expand...
I think you're required to accept 5 to 15, with 12 nominal, and required
to provide at least 10, but don't trust my memory if you're actually
implementing something. +/- 5 is definitely borderline and not
recommended.
 
Terran Melconian wrote:
In article &lt;40aad995$0$16593$5a62ac22@freenews.iinet.net.au&gt;,
Al Borowski &lt;aj.borowski@erasethis.student.qut.edu.au&gt; wrote:

A PIC I/O pin might be 0v off, 5v on, where RS232 needs -5V on, to 5V
off (I think).


I think you're required to accept 5 to 15, with 12 nominal, and required
to provide at least 10, but don't trust my memory if you're actually
implementing something.
Click to expand...
You are correct... I should have said 'at least -5V on, to 5V '. I don't
carry the RS232 standard in my head =)


+/- 5 is definitely borderline and not
recommended.
Click to expand...
The minimum threshold for reception is +/-3V, but many PC's will work
from 0V-5V. While you shouldn't make a product that way, for hobby use
its probably fine.

http://www.lammertbies.nl/comm/info/RS-232_specs.html

cheers,

Al
 
On Wed, 19 May 2004 13:59:54 +1000, the renowned Al Borowski
&lt;aj.borowski@erasethis.student.qut.edu.au&gt; wrote:

Iftikhar wrote:
Whats the purpose of Level Shifter.

MAX3232, etc...

RS232 voltages are not the same as microcontroller voltages.

A PIC I/O pin might be 0v off, 5v on, where RS232 needs -5V on, to 5V
off (I think).

Al
Click to expand...
I believe 0-5V works on all common (maybe all known) receivers (for a
short distance and with other caveats). However, the MAX232 etc. not
only level-shift but also invert, so using logic levels direct from a
microcontroller really only works if both sides agree to eschew the
transceiver or if you bit-bang the serial interface. I don't know of
any microcontroller hardware UART that has the option of inverting the
signal levels.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
In message &lt;jb4ma0lulaqcfd28u6bdgnq61d3e8kg4oh@4ax.com&gt;, Spehro Pefhany
&lt;speffSNIP@interlogDOTyou.knowwhat&gt; writes

&lt;snipped&gt;
I believe 0-5V works on all common (maybe all known) receivers (for a
short distance and with other caveats). However, the MAX232 etc. not
only level-shift but also invert, so using logic levels direct from a
microcontroller really only works if both sides agree to eschew the
transceiver or if you bit-bang the serial interface. I don't know of
any microcontroller hardware UART that has the option of inverting the
signal levels.
Click to expand...
Renesas (Mitsubishi) M16C UART 2 allows this. Handy for a quick ANSI
terminal lash-up for debugging. 0-3V3 works also, the threshold seems
to be around 2V for the several PCs I've used, and 38k4 baud seems
perfectly reliable over 5m. No, I wouldn't do this for production.

Cheers
--
Keith Wootten
 
On Wed, 19 May 2004 04:24:26 +0000 (UTC), terran@mit.edu (Terran
Melconian) wrote:

In article &lt;40aad995$0$16593$5a62ac22@freenews.iinet.net.au&gt;,
Al Borowski &lt;aj.borowski@erasethis.student.qut.edu.au&gt; wrote:
A PIC I/O pin might be 0v off, 5v on, where RS232 needs -5V on, to 5V
off (I think).

I think you're required to accept 5 to 15, with 12 nominal, and required
to provide at least 10, but don't trust my memory if you're actually
implementing something. +/- 5 is definitely borderline and not
recommended.
Click to expand...
The threshold of a 1489 is approximately +1V, so 0V to +5V signals
will work, though with marginal noise margin.

The original "specification" was for nominally +/- 10V signals.

(I know... I designed both the MC1488 and the MC1489 :)

...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.
 
On Wed, 19 May 2004 09:23:54 +0100, the renowned Keith Wootten
&lt;keithw@nononono.co.uk&gt; wrote:

In message &lt;jb4ma0lulaqcfd28u6bdgnq61d3e8kg4oh@4ax.com&gt;, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat&gt; writes

snipped

I believe 0-5V works on all common (maybe all known) receivers (for a
short distance and with other caveats). However, the MAX232 etc. not
only level-shift but also invert, so using logic levels direct from a
microcontroller really only works if both sides agree to eschew the
transceiver or if you bit-bang the serial interface. I don't know of
any microcontroller hardware UART that has the option of inverting the
signal levels.

Renesas (Mitsubishi) M16C UART 2 allows this.
Click to expand...
Cool, thanks.

Handy for a quick ANSI
terminal lash-up for debugging. 0-3V3 works also, the threshold seems
to be around 2V for the several PCs I've used, and 38k4 baud seems
perfectly reliable over 5m. No, I wouldn't do this for production.
Click to expand...
However, it would be just fine for a port used only for setup *during*
production.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
In article &lt;13dd5c27.0405181915.7cacc27e@posting.google.com&gt;,
Iftikhar &lt;radius2000@hotmail.com&gt; wrote:
Whats the purpose of Level Shifter.

MAX3232, etc...
Click to expand...

To adapt the logic levels used in modern integrated circuits to
the logic levels used in equipment designed in the early 1960s.

Mark Zenier mzenier@eskimo.com Washington State resident
 
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