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connecting two rs232 devices

Posted on 2004-09-29
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Last Modified: 2010-04-26
hello,

I have a barcode scanner which has a 9 PIN female type rs232 connector and i need to connect it to a piece of hardware which also as a 9 PIN female rs232 connector .

I bought a gender changer which has male connectors at both ends and I connected the two devices using this. It didn't work however  . The gender changer is a straight pin connector.

What do i need to connect these two devices  ?

thanks

k
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Question by:kfc23
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10 Comments
 
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Accepted Solution

by:
Callandor earned 300 total points
ID: 12179736
You need what's called a crossover or null modem cable, which swaps the transmit and receive signals.  You can buy one with the appropriate connectors at a place like www.ramelectronics.com.
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LVL 69

Expert Comment

by:Callandor
ID: 12179765
Oops - wrong link.  here's the right one: http://www.ramelectronics.net/html/nullmodem_cables.html
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Author Comment

by:kfc23
ID: 12188247
thanks for the help.

I thought null modem cables were for  two DTE devices (for instance two computers) ? what about hand shaking etc ?

I have a barcode scanner which I'm trying to connect to a device which runs an embedded java app . The java app simply  reads barcode strings sent over rs232 .

I'm just making sure the null modem cable is the correct option before I go out and buy it .

thanks again.

ken



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LVL 69

Expert Comment

by:Callandor
ID: 12189533
There's only two standard ways that I know to connect RS-232: the straight way you tried, and using a null modem.  There is always the possiblity that one or both of these devices do not communicate using standard communications protocols.  Did you get a manual that describes how to communicate with them?  You can try hooking them up to a PC and analyzing them with a program like LookRS232.
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Author Comment

by:kfc23
ID: 12189659
the scanner works fine when i connect it to my pc and use hyper terminal. I've also had no problem with using a different type of scanner ( with male type connector ) connected to the module running my java app .

I'll go ahead and try the null modem.

thanks for the help.
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LVL 1

Expert Comment

by:Binsky
ID: 12234929
You'll probably have solved it with the nullmodem cable, but to verify this you could check out the pinning of the barcode scanner port and the hardware's port. If they have their RX (receive) and TX (transmit) signals on the same pin (number), you can be sure you need a nullmodem cable.

And you were right, this cable is also used to create a serial connection between two pc's, but can also be needed to connect some pieces of hardware together.
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Expert Comment

by:Binsky
ID: 12850453
No objections from me! Good answer!
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