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With this configuration the TD320 will have control of the transit of
the data of the corresponding port. For each of the two ports, there
can be active up to 256 frames (active packets) at the same time.
Each frame corresponds to an instruction of direct communication:
•
Reading from a Slave:
Reading from the slave at the
ModBus address corresponding to the data of interest is
memorized in the registers of the Master. Each instruction can
read up to 16 consecutive words.
•
Writing on a Slave:
Data of interest by the Master is written in
the slave at the ModBus address corresponding to the data to
overwrite. Each instruction can write up to 16 consecutive
words.
•
Read/write on a Slave:
Normally data read from the slave is
saved in the Master. When the data internal to the TD320
varies by effect of the program, it is useful to write the modified
data into the Slave. Each instruction of read/write can operate
only on 1 word.
6.2.2 ModBus RTU Slave
The protocol ModBus Slave can be configured for all three of the
ports COM1, EXP1, and COM2.
With this configuration all of the resources of the terminal are
available to the Master device that is eventually connected.
The following table indicates all of the data (word and bit)
accessible by use of the ModBus protocol. Each area of memory
corresponds to a distinct ModBus address (for the access of a
word or a bit), variable from 0 to 65536.
The read/write access and the value given at startup of the TD320
are shown for each. Depending upon the initialization values, the
following cases occur:
