BCU-02 ABB control unit 3AUA0000110429 kit stock

Description

BCU-02 explains several related problems:
1) Some field buses BCU-02 use tokens to solve the problem of bus control.
It is easy to think that if the slave station needs to serve the master station for urgent matters, but MODBUS has stipulated polling rules, it may be too late when you wait. So many fieldbuses invented a special thing called token. The token is very short, only one byte, and it can be passed quickly on the bus. The token is passed in each site. The master station is the one who gets the token and can publish information. If this site has nothing to publish, it will give the token to the next site, thus solving the bus occupation problem.

2) In case of open circuit in the link, BCU-02 can adopt dual master stations to avoid communication interruption. The two master stations (RS485 interfaces of the two master stations of PLC) are connected with handshake lines. At ordinary times, the main RS485 is opened, while the auxiliary RS485 is floating. Although the floating RS485 is connected to the bus, it is in a high resistance state, which is equivalent to complete disconnection. In case of open circuit, the slave station will immediately open communication after confirmation, and connect communication from both ends of the link.
Sometimes, circular communication measures are taken. Limited to space, no introduction.
3) MODBUS can work on the network layer. At this time, the BCU-02 protocol changes to MODBUS-TCP, but it still conforms to the master-slave structure.
4) The MODBUS protocol was invented by Modicon Company in the United States. The company’s purpose is that the MODBUS protocol is a free public agreement. Later, Modicon was acquired by Schneider. Schneider inherited the practice of Modicon. MODBUS is a free public agreement. Since MODBUS has become Schneider’s protocol, Schneider has extended it to the network layer to build the MODBUS-TCP protocol of the network layer and the internal dedicated MODBUS-PLUS protocol. Due to space limitation, the description of these two agreements will be omitted here.
5) Differences between RS232 and RS485
People who have studied analog and digital electronics know differential circuits. The differential circuit has a common mode rejection ratio, which can eliminate common mode errors. RS485 interface has this feature. Therefore, the transmission distance of RS232 interface is only ten meters, while that of RS485/RS422 interface is 1200 meters.

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