Searching \ for ' Serial port drive specs. Noncomliant dev' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/io/serials.htm?key=serial
Search entire site for: 'Serial port drive specs. Noncomliant dev'.

No exact or substring matches. trying for part
PICList Thread
'[PICLIST] Serial port drive specs. Noncomliant dev'
2001\06\14@121405 by Robert Rolf

picon face
Hi Gang,

I'm using an opto isolator on my RS232 comm lines to a PIC system.
I have discovered that many portable computing devices DO NOT MEET the
RS232 spec in that their maximum output is 5V, rather than the 12V
of the spec. Since I have to design for 'worst case' has anyone
encountered devices that put out less that 5V and 10mA when
signalling, or more than 12V and 30mA of the spec limit?

TIA

Robert

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email spam_OUTlistservTakeThisOuTspammitvma.mit.edu with SET PICList DIGEST in the body


2001\06\14@123117 by David VanHorn

flavicon
face
At 10:12 AM 6/14/01 -0600, Robert Rolf wrote:
>Hi Gang,
>
>I'm using an opto isolator on my RS232 comm lines to a PIC system.
>I have discovered that many portable computing devices DO NOT MEET the
>RS232 spec in that their maximum output is 5V, rather than the 12V
>of the spec.

They are only required to deliver 3V into a standard load.


--
Dave's Engineering Page: http://www.dvanhorn.org

I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here
in my signature line, but due to the inability of sysadmins at TELOCITY to
differentiate a signature line from the text of an email, I am forbidden to
have it.

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email .....listservKILLspamspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body


2001\06\14@123311 by Don Hyde

flavicon
face
Many (we won't get into HOW many) years ago I worked with original Data
General Nova computers.  They really cheaped out and used standard TTL gates
(high around 4.7V, low around 0.3V) for the "rs232" interface.  It mostly
worked.  Palm uses a similar cheat to this day, with CMOS drivers and
receivers.

Ever since those days, I have tried very hard to make sure my rs232 outputs
were strictly kosher, and that my inputs were tolerant of anything remotely
resembling a legal signal level.  And NEVER count on getting any useful
power from the other end of the wire.

It's sooooo easy these days with cool chips like the MAX232 that I wouldn't
waste a minute considering any other way.  Maxim and other vendors have
whole families of teensy, low cost, easy-to-use, well-engineered chips that
really do the job right.

Figure out a good way to slip a little power past the isolation to a little
island containing the RS232 interface, then isolate it at the logic-level
interface with the optos or whatever you like.

> {Original Message removed}

2001\06\14@123728 by Douglas Butler

flavicon
face
A lot of new RS232 chips are only spec'd for +/- 3V output.  I would use
3V 5mA as a lower limit.

Douglas Butler (aka Sherpa Doug)
Senior Engineer
Imetrix Inc.
1235 Route 28A
P.O. Box 152
Cataumet, MA 02534-0152
tel. (508) 564-6460
Fax (508) 564-6860
dbutlerspamKILLspamimetrix.com

> {Original Message removed}

2001\06\14@125836 by Alan B. Pearce

face picon face
>Many (we won't get into HOW many) years ago I worked with original Data
>General Nova computers.  They really cheaped out and used standard TTL
gates
>(high around 4.7V, low around 0.3V) for the "rs232" interface.  It mostly
>worked.  Palm uses a similar cheat to this day, with CMOS drivers and
>receivers.

This is true of not only those systems mentioned, but many others as well.

As someone else pointed out, at the receiving end you can count on only 3V,
and as the spec is that the load should be no less than 3kohm, you should
not count on more than 1mA. There are opto's around that will operate at
this low level of current.

If you are trying to draw 10mA or more then expect the volts to sag, as the
source impedance is expected to be around 300 ohms to limit waveform rise
and fall times, and so limit crosstalk problems in long cables.

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email .....listservKILLspamspam.....mitvma.mit.edu with SET PICList DIGEST in the body


2001\06\14@131454 by Ron Wilder

flavicon
face
check out the Dallas 275.  These are 8-pin devices and only need +5V.  The
other voltages are obtained via the rx signals!
Ron

"Alan B. Pearce" wrote:

{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body


2001\06\14@175712 by Lee Jones

flavicon
face
> I'm using an opto isolator on my RS232 comm lines to a PIC system.
> I have discovered that many portable computing devices DO NOT MEET the
> RS232 spec in that their maximum output is 5V, rather than the 12V
> of the spec.

RS232 has been EIA/TIA-232 for a decade or so.

The spec states that the signal levels at the transmitter must
be +5 to +15 volts or -5 to -15 volts.  The signal level at the
receiver must be +3 to +25 volts and -3 to -25 volts.

EIA-232 is voltage (not current) based.  Transmitter must drive
a receiver impedence of 3K to 7K ohms and transmitter must be
able to tolerate a short circuit output, so don't expect much
current capability.
                                               Lee Jones

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email @spam@listservKILLspamspammitvma.mit.edu with SET PICList DIGEST in the body


2001\06\14@234449 by Bob Ammerman

picon face
Don,

I go way back with the NOVA's myself (about 1973). I even worked for DG for
a couple years. Which serial port implementation didn't provide proper
swing?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

Which o
----- Original Message -----
From: "Don Hyde" <KILLspamDonHKILLspamspamAXONN.COM>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Thursday, June 14, 2001 12:30 PM
Subject: Re: Serial port drive specs. Noncomliant devices?


> Many (we won't get into HOW many) years ago I worked with original Data
> General Nova computers.  They really cheaped out and used standard TTL
gates
> (high around 4.7V, low around 0.3V) for the "rs232" interface.  It mostly
> worked.  Palm uses a similar cheat to this day, with CMOS drivers and
> receivers.
>
> Ever since those days, I have tried very hard to make sure my rs232
outputs
> were strictly kosher, and that my inputs were tolerant of anything
remotely
> resembling a legal signal level.  And NEVER count on getting any useful
> power from the other end of the wire.
>
> It's sooooo easy these days with cool chips like the MAX232 that I
wouldn't
> waste a minute considering any other way.  Maxim and other vendors have
> whole families of teensy, low cost, easy-to-use, well-engineered chips
that
> really do the job right.
>
> Figure out a good way to slip a little power past the isolation to a
little
> island containing the RS232 interface, then isolate it at the logic-level
> interface with the optos or whatever you like.
>
> > {Original Message removed}

2001\06\14@235728 by Bob Ammerman

picon face
They are required to deliver +/-5V IIRC, the receiver is required to treat
+/-3V or more as valid. This gives 2 volts of noise margin.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

More... (looser matching)
- Last day of these posts
- In 2001 , 2002 only
- Today
- New search...