USS (Universal Serial Interface, or Universal Serial Communication Interface) is a communication protocol developed by Siemens specifically for drive devices. It has also experienced a continuous development and improvement process over the years. Initially, USS was used to parameterize the drive, which was more oriented towards parameter setting. It is widely used in the connection between the drive unit and the operation panel and debugging software (such as DriveES / STARTER). Recently, due to its simple protocol and low hardware requirements, USS is also increasingly used to communicate with controllers (such as PLCs) to achieve a general level of communication control.
Note: USS provides a low-cost, relatively simple communication control method. Due to its own design, USS cannot be used in applications that have high requirements on communication rate and data transmission volume. In these high communication requirements, you should choose a better real-time communication method, such as PROFIBUS-DP. This limitation of USS must be considered when designing the system.
For example, if in some applications with high speed synchronization requirements (such as paper production lines), USS communication control is adopted for dozens or even dozens of inverters, the effect can be imagined.
The basic features of the USS protocol are as follows:
Supports multi-point communication (thus can be applied to networks such as RS 485)
A single-master "master-slave" access mechanism
There can be up to 32 nodes (up to 31 slaves) on a network
Simple and reliable message format, making data transmission flexible and efficient
Easy to implement and low cost
The working mechanism of USS is that the communication is always initiated by the master station. The USS master station continuously polls each slave station, and the slave station decides whether and how to respond according to the instructions received. Slaves will never actively send data. The slave answers when the following conditions are met:
There is no error in the received master station message, and
The slave station is addressed in the message received from the master station
The above conditions are not met, or the master station sends a broadcast message, and the slave station will not make any response.
For the master station, the slave station must send back a response within a certain time after receiving the master station message. Otherwise, the master station will be regarded as an error.
USS character frame format
The character transmission format of USS conforms to the UART specification, that is, it uses serial asynchronous transmission. The character transmission frame of USS on the serial data bus is 11 bits in length, including:
Consecutive character frames make up the USS message. In a message, the interval delay between character frames is less than the transmission time of two character frames (of course this time depends on the transmission rate).
The free port communication mode of S7-200 CPU can just support the character frame format mentioned above. By defining the free port of S7-200 as the above character transmission mode, it can be programmed to send and receive USS protocol messages. The communication mode supported by the master controller must be consistent with the requirements of the drive to be controlled. This is the basis for the communication between S7-200 and Siemens drives.
USS message frame format
The USS protocol messages are concise and reliable, efficient and flexible. The message consists of a series of characters, and their specific functions are defined in the protocol:
Each cell above represents one character (byte). among them:
STX: start character, always 02 h
LGE: packet length
ADR: Slave address and message type
BCC: BCC check character
The data bytes between ADR and BCC are called USS net data. The data exchanged by the master and slaves are included in the net data area of ​​each message.
The net data area is composed of the PKW area and the PZD area:
Each cell above represents a word (two bytes).
PKW: This area is used to read and write parameter values, parameter definitions, or parameter description text, and can modify and report parameter changes. among them:
PKE: parameter ID. Including the information representing the command and response of the master station, and the parameter number, etc.
IND: parameter index, mainly used for positioning parameters in conjunction with PKE
PWEm: parameter value data
PZD: This area is used to transfer control and process data between the master and slave stations. The control parameters correspond to the round trip between the master and slave stations according to the set fixed format. Such as:
PZD1: Control word sent from master to slave / status word returned from master to master
PZD2: Reference given by the master station to the slave station / actual feedback from the slave station back to the master station
PZDn: ...
Depending on the type of data transferred and the drive device, the data lengths of the PKW and PZD areas are not fixed, and they can be flexibly changed to suit specific needs. However, when used for automatic control tasks to communicate with the controller, all nodes on the network must work according to the same settings and cannot be changed at will throughout the work.
2000W Digital Tv Transmitter,Wireless Fm Digital Transmitter,2Kw Wireless Digital Tv Transmitter,2Kw Video Digital Tv Transmitter
Anshan Yuexing Technology Electronics Co., LTD , https://www.yxhtfmtv.com