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The PROFIBUS bus is a purple shielded twisted pair cable, with the two cores being red and green. When connecting to the bus connector, the wiring must be done according to color, generally A1 and A2 are green, while B1 and B2 are red.
2. Devices on the PROFIBUS bus are connected in a series (A1-A2, B1-B2), so both devices at the ends are connected to the incoming side of the bus connector (A1 and B1, with A2 and B2 left open). The intermediate devices connect the incoming lines to A1 and B1, and the outgoing lines to A2 and B2.
3. The position of the termination resistor switch is set to “ON” for the devices at both ends (the devices that only have incoming lines), while the intermediate devices are set to “OFF”. The reason is as follows: each bus connector has a 200-ohm termination resistor, and only the devices at the ends need to connect the termination resistor. The purpose is to match the impedance on the bus and reduce signal attenuation. When the termination resistor is in the “ON” position, A1 and B1 are connected to the termination resistor and disconnected from A2 and B2. When the termination resistor is in the “OFF” position, A1 and B1 are disconnected from the termination resistor and connected to A2 and B2.
4. After wiring is complete, it is best to use a multimeter to check the connections. A1, B1, and the terminal points 3 and 8 of the bus connector should be connected, so you need to measure the continuity between the terminal points 3 of both ends and between terminal points 8, and check if the resistance between 3 and 8 is around 110 ohms (since both ends are connected to the termination resistors, it is equivalent to two 220-ohm resistors in parallel).
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