semaphore TBOX LT2-530 Series, Руководство пользователя, Страница: 137 / 197

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Trigger: Select a digital Tag that will trigger the communication, according to a ‘Condition’ (see
next). Working with several equipment, you declare different Tags and then control
differently the communication to each equipment.
The Trigger must be a digital variable (DIV).
Condition: Condition of Tag ‘Trigger’ to start communication. Typically, you will work with a
permanent connection (Trigger in High or Low state). Or you can decide to execute one-
shot communication, on edge changing of the Tag Trigger.
The changing of state of the Tag can be controlled by BASIC, Ladder, or Periodic events.
15.2. Creating a ModBus Transaction
Example: reading of 8 ‘floating’ variables in Slave22 starting at address 168
Tag: Select an existing Tag by clicking the button. Be sure you select a Tag of the same type
than the one you want to access in the ‘Slave’ (Byte, Word, DWord or Float).
If the Tag does not exist, you can create it after having clicked the button. It is the Tag of
the Master; it contains the value you want to write in a Slave or it is a register that contains
the value that Master reads in a Slave.
In case of block communication (with a quantity > 1), this Tag is the one of first ModBus
address.
Operation :
Operations MASTER (Tag) SLAVE (Address)
READ Data
WRITE Data
Read: the Master reads data from the Slave.
Write: the Master writes data to the Slave.
Quantity : Quantity of variables of successive addresses that are read (or written) in the Slave. It depends
on the external source, the types of variable and the ModBus function used (see tables
below).
ModBus protocol handles only words (16 bits). When working with 32 bits, TWinSoft
adapts the quantity to double the number of words. 32 bits variables are handled with:
<Hi word1><Lo word1><Hi word2><Lo word2>… It can be adapted from the “Advanced…”
properties of the remote device.