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The effective transfer of the data in the serial line is executed in a
manner that is independent to the normal scan of Ladder code, in
different times according to the port that is used.
6.1.1 Ports COM1 and EXP1
The ports COM1 and EXP1 can be configured with protocol
ModBus (master or slave), or Nais Matsushita master, Control
Technique. These are the ports typically used for communication
with other devices (PLC, etc.).
The control of the communication is carried out every 1 mS
.
This means that the corresponding flow of serial data will be
controlled 1000 times a second.
6.1.2 Port COM2
The port COM2 can be configured only by using protocol ModBus
slave. This port is used for programming the terminal by PC.
The control of the communication is carried out every scan
cycle of the Ladder code
.
This means that the flow of the data in the serial port COM2 will be
controlled one time at the end of each scan cycle.
6.2 Protocol ModBus RTU
The ModBus on the serial line is a Master-Slave protocol
. In a
network with this type, there is a single node (the Master) that
interrogates and commands the Slaves and processes the results.
The Slave nodes typically do not transmit data unless specifically
requested by the Master and do not communicate directly between
each other.
A device in the serial line (a network node) is uniquely determined
by an identification number (ID, variable from 1 to 255), called the
ModBus Slave address: two devices cannot have the same
address.