Photocoupler

Fool tutorial] PROFIBUS-DP communication distance and the use of repeaters

The relationship between communication distance and baud rate of PROFIBUS-DP:

Since the communication length of the PROFIBUS protocol is limited by the baud rate, in the process of using PROFIBUS communication on site, it is often the case that a certain transmission rate is guaranteed, but the bus exceeds the specified length. In this case, RS485 relay is required. Device.

• Automatically search data transfer rate

  • Data transfer rate 45.45 kbit/s

  • 24 V DC power display

  • Display bus status for segment 1 and segment 2

  • Isolate segment 1 and segment 2 by switch

  • When the terminating resistor is turned on, the segment on the right can be isolated

  • Decoupling segment 1 and segment 2 during static interference on the line

  • Increase the number of sites and extended distance

  • Optical isolation between segments

  • Debug startup help

  • Switch for disconnecting the segment

  • Display bus activity

  • Isolate segments that are incorrectly inserted into the terminating resistor

  

  The use of the repeater is:

  Repeaters need to increase the distance, only between the upper and lower.

  One bus does not connect, and the resistor hits ON.

  The MODE switch is the most important and cannot be turned OFF.

  [analysis]

  “The repeater needs to increase the distance, and it can only be used between the upper and lower sides.” The repeater only amplifies between the upper and lower bus segments. As shown in Figure 1, the repeater can be connected to four DP cables, the corresponding terminals are A1B1, A1'B1' and A2B2, A2'B2', where A1B1, A1'B1' are bus segment 1, A2B2, A2 'B2' is bus segment 2. Only the data signal between bus segment 1 and bus segment 2 is amplified.

  

  Figure 1 PROFIBUS RS485 repeater panel diagram

  "A bus does not connect, the resistor hits ON". It can also be seen from its internal circuit diagram (Fig. 2) that the terminal with the terminal number is only shorted because the same signal is shorted between the left and right, so there is no signal. Amplification. The second sentence is the setting of the terminating resistor on the repeater. As can be seen from Figure 1, there are two terminating resistors S1 and S2 on the repeater, corresponding to bus segment 1 and bus segment 2, respectively. As can be seen from Figure 2, if the terminating resistor is turned to the ON position, a resistor is connected between the bus AB, and the terminal with the terminal number is disconnected from the terminal of the same group. Therefore, if the repeater is the last station on the bus of the network segment, connect the DP bus to the terminal with no terminal number and turn the terminal resistance to the ON position. If the bus is only connected to A1B1, the terminating resistor S1 will be turned to the ON position. If only A2B2 is connected, the terminating resistor S2 is turned ON. If the four terminals of a bus segment are wired, the corresponding terminating resistor is not activated.

  

  Figure 2 Internal circuit diagram of PROFIBUS RS485 repeater

  Figure 3. Figure 4 and Figure 5 illustrate the length of the cable that the repeater can extend and the setting of the terminating resistor in different wiring modes (assuming the transmission rate is 1.5M bit/s).

  image 3

  

  Figure 4

  

  Figure 5

  "The MODE switch is the most important and cannot be turned OFF." The MODE switch in the middle of the repeater is the switch that the repeater works. If it is turned to the OFF position, the bus segment 1 and the bus segment 2 are completely separated. There is no signal at all, and there is no signal amplification function.