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I have a device that i want to connect with, reading the user's manual it claims that i can connect to the device via SR-232 interface and it list all the steps to configure a null modem connection on widows 7 an use that connection with its own software, so far so good, the only problem i have is that most null modem connections that i have seen on the internet, are done with cables like these:

but the device does not have a port like that, instead it has a port like this: , thats right its like a phone jack with a label below it that says "RS232", so i was wondering if i need a special cable ? because my computer does not have an entry like that

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That 'phone jack' is probably an RJ-45 type connector (usually 8 wires), it looks like an oversized 'phone plug' (which is an RJ-11 type, max 6 wires). And @Ignacio (hey!) is correct about the wiring. – lornix Jul 6 '12 at 6:03
up vote 0 down vote accepted

Not a special cable, but a special adapter. 4 signal lines is enough to run a RS-232 connection, but they need to be wired to the appropriate pins on the D-Sub connector. Example here, but use the pinout appropriate for your device.

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