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Re: Serial Port Bug?



Tim wrote:
> On Tue, 2007-11-27 at 08:48 -0700, Karl Larsen wrote:
>>     With a volt meter I find some pins have a constant -10.7 volts on 
>> them which is the standard RS-232 for a no-data signal. In this static
>> measure the voltmeter sees no positive volts near +12 volts. 
> 
> NB:  It's quite common for serial ports on computers, these days, to be
> nothing like "standard RS-232".  That can be a problem for some devices
> that you want to connect to it.
> 
> I'd be trying some tests by connecting two computers together, and
> seeing what you get.  Or plugging in an old modem, and doing the old ATI
> command tests, etc.
> 
I thought the standard for RS-232 was +/- 3-15 volts, with a
requirement that the device be able to handle +/- 25 volts. Even
though you may have 15 volts on one end, you have to allow for
voltage drop on long runs.

I am used to seeing +/-12v and sometimes +/-5v depending on the
supply available. Depending on the state of a port, I would not be
at all surprised to see all negative voltages to ground. Remember, a
negative voltage is a logic 1, so the status and data line will all
be negative when the port is ready. (TD, DTR, RTS)

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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