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Ext modem doesn't work,when the serial cable is changed.

Posted on 2003-11-12
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Last Modified: 2013-12-27
The mode type is 56K smart SCM modem by DYNAMODE.
OS: windows 98 SE

I have this modem and he works greate.
the problam is that the cable i recieved with it,serial cable,is too short about 0.5 meter/20 inch.
so i bought a new one 1.8 meter/71 inch.

but surprisely it just dosn't work good.
i can't dail from the dailer and get error meseges.

i've tried the cable on an old  serial cable and it works good.

thank you for the help. :)
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Question by:swift87
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Expert Comment

by:Huseyin1
ID: 9730800
Hi

Do you have to have this long cable, baybe there is an atenuation issue here and the distance is simply too long, its like the IDE cable limit of 18inches, anything over that and the device at the end of the cable wont work.

I suppose you can look for interference on your desk, if this 1.8 meter wire is passing any lamps and other electrical iteams then this could be the problem, move those iteams out of the way, or put the modem somewhere else, or simply get an internal one.

H
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Author Comment

by:swift87
ID: 9732081
Hi
I would prefer to put it somewere else,so yes i have to have this cable.

there're no object or electrical iteams in the way of the cable.

you have agood point by comparing it to an IDE cable.

i'll chack it out.
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Expert Comment

by:war1
ID: 9732565
Greetings, swift87!

Have you tried another cable 1.8 meter cable, or a shorter one?  Some modem are designed to work with a certain hardware, including cable.  Check if the cable reqires shielding.

Best wishes, war1
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Author Comment

by:swift87
ID: 9744842
hi
i dont have another 1.8 meter but i assume the result shall be the same.

"designed to work with a certain hardware, including cable"

serial cable is serial cable, no matter how you look at it.execpt for the length,as mentioned above.

anyone knows the limet of an ext' modem or device cable,or anything related to this matter?

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by:lidsky
ID: 9780278
swift87,

"but surprisely it just dosn't work good."
"i can't dail from the dailer and get error meseges."

Do you mean it works sometimes or it never works.

If it never works I would suspect that either the cable is defective or what you have is a null modem cable, used for programs like laplink, where the receive transmit signals are crossed over.

RS-232 specification is 50 feet max @ 20kbs, however, I know of many places where this has been greatly exceeded without problems. Therefore, a 6 foot cable should work.
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Author Comment

by:swift87
ID: 9789616
"Do you mean it works sometimes or it never works."

windows(98) recognize it ,in the device manager thats it for working.
 
"If it never works I would suspect that either the cable is defective or what you have is a null modem cable, used for programs like laplink, where the receive transmit signals are crossed over."

i chacked it with a serial mouse and the mouse works fine, so how could it be defective or a null modem?

"RS-232 specification is 50 feet max @ 20kbs..."

50 feet = 15.24 meter
this new finding just confuse me more
and i thought 1.8 meter is long... :O



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Accepted Solution

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lidsky earned 250 total points
ID: 9790071

The cable can still be defective, even if a mouse works with it.
A mouse only uses pins 2, 3, 4, and 7.
The modem uses pins 2, 3, 4, 6, 7, and 8.
If the conductors on pins 6 or 8 are broken the modem will not work.

My best guess is that the conductor between pins 6 are broken.
Pin 6 is DSR (data set ready), it tells the serial port that the modem is powered on.

I suggest you buy a new cable, and try it, they don't cost very much.
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Expert Comment

by:lidsky
ID: 9790332

And another thing. Once the modem has been configured into the system, device manager will always show the device as working. Even if you disconnect it.
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Author Comment

by:swift87
ID: 9790911
Thank toy very much lidsky
your knowledge is more than impressive :)
i'll  chack it and come back.

May i ask, how do  you know\remember the pins number and uses,for it's like remembring each and every hair on my haed #:-)
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Expert Comment

by:lidsky
ID: 9791047
swift87,

I don't remember all this, I only know how/where to find the information. :-)

Some of it I find on the WEB and some of it in reference manuals that I have.
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Author Comment

by:swift87
ID: 9891774
Hi
I chacked and some of the pins you have mentioned such as 6 weren't connected.

so i gonna build a new cable.

You said The modem uses pins 2, 3, 4, 6, 7, and 8.well i searched alot of webs regarding this and i couldn't find somting like this.what about pins 1 and 5 aren't they necessary?cause they stand for Carrier Detect and System Ground respectively.
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Author Comment

by:swift87
ID: 9891824
i checked the  short cable of the modem now and all the pins are connected to wires.
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Expert Comment

by:lidsky
ID: 9907904
swift87,

It seems the information I gave you came from a source which was in error.
You're quite right about pins 1 and 5 (DCD,SignalGround).

You can find the correct pinouts at - http://www.zytrax.com/tech/layer_1/cables/tech_rs232.htm

Anyway, it looks like you have a bad cable.
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Author Comment

by:swift87
ID: 9916499
THANK YOU EVERYTHING!:)
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Expert Comment

by:lidsky
ID: 9916662

Glad to be of help.
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