Monday, March 5, 2012

The Protocol Serial Interface of Fatek PLC

Master and Slave
FATEK PLC is described as the slaves in the peripheral devices communication that are always described as masters when correspond with FATEK PLC. All of the peripheral devices transfer the message when they correspond with FATEK PLC and it reacts when accepting the message from masters.

The FATEK PLC Communication Message Format
There are 6 columns the data in the communication format the FATEK PLC including response (slave) and command (master) message.

1. STX (Start code): The code of hexadecimal the STX in code the ASCII is 02H. The initiate characters are all of the STX in command and reaction message. The accepting site can decide the code of data start with STX.
2. The slave station number: They are hexadecimal value of two-number. There is only station master and are 255 stations of slave in the communication frame of PLC. Each slave station has only number from 1 to FEH. When the master desires to transfer command to one or all it deals the station number task. The slave will transfer its own station number when it transfer reply message to master.
3. Code of Command: There are 2 numbers of commands for systems of hexadecimal. It is the accomplishment the slave to perform. For instance, to write or read the discrete status, setting force, run, stop, etc.
4. Data information: It includes 0 (no data) to 500 character of ASCII. The data in this column is to allocate the value or address for writing or reading. The starting of this data information includes the fault code in the response message. In usual conditions (no fault occurred), the code of error have to be 0 (30H) in the starting and then follow the status of responding or value in the message response. When error occurs, it will be the fault code instead of 0 (30H) and it will not follow the information data.
5. Checksum: it checks the value of hexadecimal ASCII code in the earlier 1 to 4 columns and creates one value of checksum in one byte length with Longitudinal Redundancy Check (LRC) method. This message will be verified with the same method at the receiving side when the message is accepted. It means the data transmitted correctly when the two check values are the similar. If the two values checked are different, there are some blunders that occurred. The LRC method calculation is to add all the value of hexadecimal (8 bits length) of code ASCII and ignore to take the number to maintain the value check at 8 bits length.
6. ETX (End code): The EXT code of hexadecimal code ASCII is 03H. The either command of EXT code or response is all ETX. It means the transmission of data terminated and begins to process data or command when the receiving side accepts the code of ETX.

• Sending and receiving message format are the same.
• Column of data in some commands may not available, and checksum will require on earlier 1 to 3 columns.
• The station number default value for PLC is all 1.


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