What is the use of PROFIBUS Terminator? -Solutions - Huaqiang Electronic Network

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Q: What is the purpose of a PROFIBUS Terminator, and when should it be used?

Question added: I'm referring to this specific device, not just a regular DP connection port. The part number is 6ES7972-0DA00-0AA0. Based on what I've been told and what I've seen on-site, there are no DP stations connected to this PROFIBUS network. Instead, it's being converted to RS485 for signal activation, and that’s why the terminator is used.

A: The main functions of a terminating resistor in a PROFIBUS network are as follows:

1. It helps maintain an idle voltage level of approximately 1.1V on the bus, which ensures stable communication.

2. It matches the impedance of the bus line (typically 150Ω) to prevent signal reflections, which can cause data errors or communication issues.

When a station is powered down, the absence of the terminator can lead to several problems:

1. If the two 390Ω resistors are removed, the bus idle voltage may drop significantly, around 0.62V, making the bus more vulnerable to electrical noise and interference.

2. The mismatch between the terminal impedance (110Ω) and the line impedance (150Ω) can create reflected signals, which may result in distorted or corrupted data transmission.

The terminating resistor should be installed at the end of the PROFIBUS DP network, similar to how standard resistors are used. However, in this case, three resistors are connected in series: 390Ω, 220Ω, and 390Ω. The DP bus connects to the 220Ω side, while the other ends are connected to the power supply. Typically, the 220Ω side will have a voltage of about 1V, and the 5V power supply is used for the DP interface (pins 5, 3, 8, and 6).

Regarding the position of the terminal resistance switch: the device at both ends of the bus (i.e., the devices that only connect to the line) should have the switch set to "ON," while the devices in the middle should be set to "OFF." This ensures proper termination and signal integrity throughout the network.

This setup is crucial for maintaining reliable communication, especially in environments where signal stability is essential. Always double-check the configuration based on the specific network layout and equipment requirements.