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Home > Forums > Electrical / Electronic Engineers > Activities > Circuit Design Forum

typical RS-232 for PC

Read More Threads Like This One

balutan (Electrical)

21 Apr 10 15:37

Copied from wiki about RS-232, "the standard requires the transmitter to use +12V and −12V, but requires the receiver to distinguish voltages as low as +3V and -3V. Some manufacturers therefore built transmitters that supplied +5V and -5V and labeled them as "RS-232 compatible."

At what voltage rail does the RS-232 on PC transmit (typically)?

MikeHalloran (Mechanical)

21 Apr 10 16:33

Actual IBM-PC used +/-12, but you can't rely on a generic PC to do that, because many, many of them didn't.

Also; the nature of your question suggests that you intend to steal some current from the RS-232 interface. Get the idea out of your head; many of them will barely light a small LED, much less power receivers and logic in your box.

Mike Halloran
Pembroke Pines, FL, USA

itsmoked (Electrical)

21 Apr 10 16:55

It's all over the map as it depends on lots of things.

Keith Cress
kcress - http://www.flaminsystems.com

MacGyverS2000 (Electrical)

21 Apr 10 16:56

Assume the PC meets minimum specs (+/-3V) and be done with it. Thinking otherwise is just a guess and will come back to bite you in the rear when you least expect it.

Dan - Owner
http://www.Hi-TecDesigns.com

zzzjim (Electrical)

29 Apr 10 17:53

Plenty of newer PCs and laptops no longer have the voltage to run 5V logic from RAW Handshaking lines .
10 years ago these sat at +/-  7 to 9 volts

RS-232 Tx-Rx  ICs even had 232 in their names .

Assuming any better than +/- 3V will work
    .. when it feels like it !

  ( measure actual equipment to be used for clues )

ScottyUK (Electrical)

30 Apr 10 3:32

Just think about how many modern PCs don't even have an RS-232 port, let alone a full-spec port. You are designing for a rapidly shrinking market. Anyway you can get more power and better speed out of a USB interface, and most computers of today have at least one USB port.

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If we learn from our mistakes I'm getting a great education!

benta (Electrical)

30 Apr 10 9:57

Scotty, I don't think you'll find ANY computer today without a USB port.

Benta.

IRstuff (Aerospace)

30 Apr 10 10:15

Only if you don't consider the iPad to be a computer...

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

MacGyverS2000 (Electrical)

30 Apr 10 15:14

I don't... :-p

Dan - Owner
http://www.Hi-TecDesigns.com

photoengineer (Civil/Environmental)

4 May 10 14:01

+/- 5 V

Cedar Bluff Engineering
http://cedarbluffengineering.webs.com

ScottyUK (Electrical)

4 May 10 14:43

Tell that to Allen Bradley's 1747-PIC which drew its power from the port. Damned things were 'usually' ok on a full-spec serial port, and somewhere between temperamental and plain dead on most modern ports. Ironically IBM laptop ports were among the offenders for refusing to work with this device. neutral

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If we learn from our mistakes I'm getting a great education!

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