Chapter 6 IO Unit
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The LK239 module is installed in the I/O slot of the LK backboard. The module itself provides the
MODBUS communication interface and the MODBUS terminal matching DIP switch, as shown in
Figure 6-30.
The MODBUS communication adopts a response mode: the master station sends command to one
slave station, and wait for the response from slave station. After receiving the instruction from the
master station, the slave station executes the instruction and feedback the execution results to the
master station, then wait for the next instruction. The time interval from the moment that the master
station gives an instruction to the moment that the slave station responds data is received is the
time-out value, which can be set via the user parameter
Time of Replay
.
For the RS485 or RS232 (select one from the two) interfaces for the MODBUS physical layer, the
transmission speed can be 115.2 kbps in the RTU transmission mode.
6.3.4.2 Operating Principle
The LK239 module creates the PROFIBUS-DP data area and the MODBUS data area in the data
memory, exchanges the data between the two data storage areas periodically, thus realizing the data
communication from MODBUS to PROFIBUS-DP.
The communication data of the PROFIBUS-DP master station (the CPU module) and LK239 is saved
in the PROFIBUS-DP data area. The communication data of the external MODBUS master station
slave station and LK239 is saved into the MODBUS data area. Upon the completion of the
PROFIBUS-DP data communication each time, it shall exchange the data of the two data storage
areas once according to the corresponding relationship between the PROFIBUS-DP address and the
MODBUS address.
ï‚Ÿ
Whether the slave station or the master station, the LK239 module cannot transmit
the REAL data directly by configuring the input/output data. It shall do this with the
help of Zone M, with the high-low byte sequence exchanged.
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