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Serial Port Programming

Posted on 2002-04-21
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Last Modified: 2013-11-15
I have a few questions about programming serial port devices.

1.) I have 2 serial ports on the back of my computer. I need to have more than 2 devices attached to the back of my computer. Can I use splitters to connect more devices to these ports, or do I have to install a PCI card to get more ports. Also, how many serial ports can my computer handle (Windows)

2.) How do I address each individual device (If I have multiple ones plugged in how can I specify which one I want to talk to)?

3.) The devices I'm programming simply use the power from the serial port to work. They have no chips or circut boards in them. Is there a way to identify these devices?

4.) Is there a way to control how much power is sent through the serial port?

Thanks!
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Question by:llllllllll
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Expert Comment

by:lsmgms
ID: 6958978
Hi,

You have too many questions and I have not touched serial comm for a long time.  However, I try to recall whatever I can remember, and I am mistaken please correct me.

1) I do not know how your splitter woking but if it is a passive device which I think, then you will not get more port because the signal is not "addressable".  I never tried adding a new I/O card, I think it can work but be aware the IRQ is shared among COM1/3 and COM2/4.  You can get max 4 ports.

2) Use "COM1:", "COM2:",..."COM4:"

3) The one you said is almost impossible.  It must has IC or some analog device to work with.  What are you trying to do with that device?

4) No much you can play, either:
a) If power is from RTS and DTR, then you may be able to cut half of the current, but you may have voltage drop until your device cannot work.
b) Put a resistor in between the Serial Comm and the device.

Regards
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DanRollins earned 400 total points
ID: 6959224
>> 1.) ... Can I use splitters to connect more devices to
>> these ports, or do I have to install a PCI card to get more ports.
NO, not for any type of normal serial port access.

>> how many serial ports can my computer handle (Windows)
At least 9, without doing any special device driver coding.

>> 2.) How do I address each individual device...
The device names are COM1,... COM9

>> 3.) The devices I'm programming simply use the power from
>> the serial port to work. They have no chips
>> or circut boards in them. Is there a way to identify these devices?
The device names are COM1,... COM9

>> 4.) Is there a way to control how much power is sent
>> through the serial port?
No.  I don't believe that you are supposed to draw power from the serial port.

-- Dan
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by:llllllllll
ID: 6961482
ok, thanks. Just curious: If I only have 2 ports and I can't use splitters or PCI cards, how will I add more ports?
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Expert Comment

by:DanRollins
ID: 6961501
You *can* add PCI cards that provide additional COM ports, but you can't use a splitter and expect any type of normal operation.

-- Dan
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Author Comment

by:llllllllll
ID: 6961539
ok thanks for the clarification
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Author Comment

by:llllllllll
ID: 6961541
thank you, I got scared when I heard that I could only use 4 ports (comment before your's)
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