ABB ACS880 inverter operation panel ACS-AP-W control panel with Bluetooth

Description

We found that from the ACS-AP-W electrical wiring, the links are in parallel. But from the communication point of view, the link is a chrysanthemum petal, belonging to orderly connection one by one.
Now we can summarize:
The RS485 bus network ACS-AP-W wiring mode must be chain daisy petal wiring mode, and belongs to half duplex communication mode; RS232 is a point-to-point connection mode, which belongs to full duplex communication. Whether it is RS232 interface or RS485 interface, they must comply with the communication protocol of the physical layer.

Then look at the MODBUS-RTU communication protocol:
With the physical layer communication interface, can ACS-AP-W communicate? The answer is no. The physical layer communication interface only enables the communication parties to have communication conditions. However, if neither of the two sides can understand what they say, or the way of speaking and grammatical structure of the two sides of the communication do not match, it is obviously impossible to communicate.
In the OSI model, the physical layer is above the data link layer. MODBUS-RTU protocol is the data link layer protocol. As long as both communication parties adopt MODBUS-RTU protocol, it can ensure that the communication language is a statement format that both parties can understand.
Notice the word “statement” here. The physical layer defines bytes, which are equivalent to words in the language. The data link layer organizes bytes into sentences, that is, frames. The frame specifies the syntax structure of the statements used by both sides of the communication.
MODBUS is also master-slave. The bus control of the physical layer is the same. The master-slave relationship here specifies the control right of the communication bus. The master station issues the command first to occupy the bus; Then leave the bus empty and give it to the slave station to write the response code; After the slave station completes, return the bus to the master station.

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