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serial ports

Posted on 2004-04-29
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Last Modified: 2010-04-26
I need some info on serial ports.
i know that serial ports takes in 1 byte and send it 1 bit at a time.
i can understand the situation when a modem is connected.
But now suppose my serial port is connected to a camera or microphone, which keeps sending it analog data
What does the serial port do to handle this analog data,
does it have an inbuilt a-d converter?
I am a layman, so could u explain this to me in very simple terms.
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Question by:vikasgkutty
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Expert Comment

by:mark_sangwine
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Hi,

Found this for you:

http://computer.howstuffworks.com/serial-port.htm

Hope it helps

Mark
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Author Comment

by:vikasgkutty
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i had already read tht
see, what....i want to know is

serial ports->what do they do when they get analog data.
do these CTS, DCD, DTR conventions hold good then?

Vikas
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Expert Comment

by:rid
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The serial port itself can only handle digital data, one bit at a time. The analog data must be converted into some kind of "bit-stream" and, in the PC, converted back to analog data by software. There is no A/D or D/A converter built into a normal serial port.

One would assume that analog data in this situation is compressed and coded and converted into (IP) data packets before transmission over the serial line. After being collected in the PC, some kind of software re-construction into analog data takes place. That is the only way I can imagine a (slow) phone line can handle internet radio etc.
/RID
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Author Comment

by:vikasgkutty
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in my application i have a communication product which is a box, with a single board computer and  lot of ports
2 of these ports r connected to microphone, camera
so, is there anything like dcd, cts and stuff between microphone and the box


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by:rid
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DTR = Data Terminal Ready
CTS = Clear To Send

These are serial connection flow control signals and can exist between two RS232 serial devices. If the microphone is just a microphone, I doubt it uses these signals - a mic is an analog device. The "box" you mention may be the part that converts sound signals into data packets and sends it along the serial connection to the PC - in which case the "box" may use the flow control signals when speaking to the PC.
/RID
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Author Comment

by:vikasgkutty
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ok, rid, i understand,
so what i want to know is in my application
i have a microphone connected to a serial port of the box(with single board compter)
so in this case do u think, the whole rs232 protocol might not be used at all...

from the circuite diagram , i see this

BOX...................midde connector..................microphone
male..................connectors..........................microphone
GND
9..........................8..8.................................12v+
5..........................5..5.................................12v-
6..........................3..3..................................Audio Input
7.........................6..6....................................Audio return



Hope u have got this pin diagram
see there is a cable from microphone, and another cable going from the end of tht cable to the box
and the pin diagaram is as shown above.
is this rs232 at all....or is it some other wiring
can i still use those dtr, cts conventions etc, used in rs232
basically i want to see, if i can find out , whether the microphone is powered up by the box, by reading maybe the dsr, dtr pins





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Author Comment

by:vikasgkutty
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No u see the box, is not what  mentioned
the box, is a commmunication device, it has an emddeded single board computer
so in effect the box can be treated as a pc
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Author Comment

by:vikasgkutty
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the box also has an MPEG frame grabber hardware,
which in turn has an a-d convertor that does the conversion
which is why i am so confused....what does those serial ports do..?
i have a task on hand to see, if can detect if there is power being supplied to the microphone from the box,
initially, i thought tht kind of stuff could be read from the serial ports using dtr, dsr  and all tht
but in theis sceaniro,, i dont think it could be,
dont u think so
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Accepted Solution

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rid earned 50 total points
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From the description it could be just DB9 connectors used for audio signals and mic DC feed, I mean, unless you positively know they are serial ports... If so, the mic itself must comprise some circuitry to make bits out of audio signals. The protocol used may be proprietary, depending on what the maker of this "box" found suitable. I know enough about this to create som confusion, probably; i haven't seen anything like the device you describe.
/RID
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Author Comment

by:vikasgkutty
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yes, i think u r right,
i guess u cant call them serial ports at all,
they r just db9 connectors

they doent function as serial prts at all
do u have a private email id

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Author Comment

by:vikasgkutty
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i could tell u some stuff on tht
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Author Comment

by:vikasgkutty
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i guess my whole confusion was
i didnt really see the difference between a serial port and a db9 connector
well, they seem to look the same, maybes thats why.
a serial port.rs232 strictly follows conventions, and thus allows us to do some detection,
like "is a carrrier detected?"
" is data terminal ready"
but, hey, these kind of stuff is not possible witha db9 connecter, silly me
thanks buddy, for showing unblinding me


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Expert Comment

by:rid
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Heheh... DB9 works OK as an RS232 connector on a PC, but I've seen those connectors on all sorts of equipment. My mail is in my profile.

Cheers
/RID
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