User manual

IEC61131 User and Reference Manual
April 22, 2008
139
The conflicting addresses should be corrected and then saved again. It is not required that
any corrections be made to the Conflict Table. The table only displays detected conflicts.
Modbus Addressing
The ISaGRAF Dictionary is used to assign Modbus register addresses to declared variables.
Assigning a network address for the variable in the edit variable dialog does this. To open
the Edit Variable dialog select Dictionary from the File menu in the ISaGRAF Programs
window. An example of an entry in the dialog is shown below.
Modbus registers are called network addresses in the Dictionary; see section A 10.2 setting
network addresses in the ISaGRAF User‟s Guide. In the above example Network
Address: entry is 30001. The variable SP_AIN01 is assigned Modbus address 30001.
Note that the edit variable dialog will use hexadecimal format for the network address when
the dialog is first opened. To change the format to decimal select Advanced options from
the Tools menu in the Programs window. Then click the Network addresses in decimal
option.
All analog, input or output, variables declared in the Dictionary are 32-bit format. This means
two Modbus registers will be automatically assigned to an analog variable within the
controller. Only the first register of the register pair is entered in the Dictionary for each
variable. If two registers per variable are not allotted, registers will be assigned twice and be
corrupted by the overlap. ISaGRAF only checks that each variable has a unique network
address, it is not aware that the target controller requires two registers for each 32-bit
variable.
Control Microsystems has added a dictionary check feature to detect Modbus addressing
conflicts. Selecting Workbench from the Tools menu in the Program window and then
selecting the Check Dictionary for Address Conflicts check box enables this feature.
Refer to the section Conflict Table of this manual for further details.
Modbus Addressing Rules
The Dictionary allows entry of several different types of variables. Refer to section A 10
Using the dictionary editor in the ISaGRAF User‟s Guide for detailed information on
declaring each variable type.
Variables of the types Real, Integer, Timers, Messages and Boolean may be assigned a
Modbus address. Any Modbus address may be used for each type of variable. For example,
while analog or message variables will usually be assigned to input or holding registers, they