Working with the I/O Mapping Dialog

Overview

The following is an illustration of the I/O Mapping tab of the device editor:

 

 

Description of the Elements in the Channels Area

The I/O Mapping tab provides the following elements in the Channels area if provided by the device:

NOTE: Inputs and outputs that are not used in the application are not read by the controller in online mode. To indicate that these inputs and outputs are not used, they are marked with a gray background. Any values that might appear in these gray lines are invalid.

Modifying and Fixing Addresses

This function is not available for all supported controllers. Consult the Programming Guide specific to your controller for further information.

You can modify and fix the displayed address of an output or input here in this tab. Use this to adapt the addressing to a given hardware configuration or to keep the address value even if the order of the modules is changed. By default, this would cause an automatic adaptation of the address values.

Consider that depending on the device description, you can only modify the address of the input or output, however, not that of its subelements (bit channels). Therefore, if an input or output is represented here in the mapping table with a subtree, you can edit only the address field of the uppermost entry (see the figure below: only the address field in the first line can be opened).

In order to fix the address value, select the entry in the Address column and press the SPACE bar to open the edit field. Either modify the value or leave it unmodified and close the edit field via the RETURN key. The address field is marked by an M symbol which indicates that the present value is fixed.

If the value has been modified, the subsequent addresses (up to the next fixed address) will be adapted correspondingly:

 

 

 

If you want to remove the fixation of the value, reopen the address edit field, delete the address entry, and close with Enter. The address and the identified succeeding addresses will be set back to the values they had before the manual modification. The M symbol will be removed.

Configuration of the I/O Mapping

Perform the I/O mapping by assigning the appropriate project variables to the device input and output channels each in the Variable column.

oThe type of the channel is already indicated in the Variable column by a symbol:  for input,  for output. In this line, enter the name or path of the variable to which the channel should be mapped. You can either map on an existing project variable or define a new variable, which then will automatically be declared as a global variable.

oWhen mapping structured variables, the editor will prevent that both the structure variable (for example, on %QB0) and particular structure elements (for example, in this case on %QB0.1 and QB0.2 ) can be entered.

This means: When there is a main entry with a subtree of bit channel entries in the mapping table (as shown in the figure below), then either in the line of the main entry a variable can be entered or in those of the subelements (bit channels) never in both.

oFor mapping on an existing variable, specify the complete path. For example: <application name>.<pou path>.<variable name>';

Example: app1.plc_prg.ivar 

For this purpose, it can be helpful to open the input assistant via the ... button. In the Mapping column, the  symbol will be displayed and the address value will be crossed out. This does not mean that this memory address does not exist any longer. However, it is not used directly because the value of the existing variable is managed on another memory location, and, especially in case of outputs, no other already existing variable should be stored to this address (%Qxx in the I/O mapping) in order to avoid ambiguities during writing the values.

See in the following example an output mapping on the existing variable xBool_4:

 

 

NOTE: When you are mapping to an existing variable, the initialization value of the variable is used as the default value. You can edit the Default value field only if you are mapping to a new created variable or if no mapping is specified.

oIf you want to define a new variable, enter the desired variable name.

Example: bVar1

In this case, the symbol will be inserted in the Mapping column and the variable will be internally declared as a global variable. From here, the variable will be available globally within the application. The mapping dialog is another place for the declaration of global variables.

NOTE: Alternatively, an address can also be read or written within a program code, such as in ST (structured text).

oConsidering the possibility of changes in the device configuration, do the mappings within the device configuration dialog.

NOTE: If a UNION is represented by I/O channels in the mapping dialog, it depends on the device whether the root element is mappable or not.

If a declared variable of a given data type is larger than that to which it is being mapped, the value of the variable being mapped will be assigned a truncated to the size of the mapped target variable.

For example, if the variable is declared as a WORD data type, and it is mapped to a BYTE, only 8 bits of the word will be mapped to the byte.

This implies that, for the monitoring of the value in the mapping dialog, the value displayed at the root element of the address will be the value of the declared variable - as currently valid in the project. In the subelements below the root, the particular element values of the mapped variable will be monitored. However, only part of the declared value may be displayed among the subelements.

A further implication is when you map a declared variable to physical outputs. Likewise, if you map a data type that is larger than the output data type, the output data type may receive a truncated value such that it may affect your application in unintended ways.

IEC Objects

This part of the tab is only available if implicitly a function block instance of a device has been created, which can be accessed by the application (for example, in order to restart a bus or to poll information). Whether such an instance is available and how it can be used, depends on the controller. Consult the Programming Guide specific to your controller.

Bus Cycle Options

This configuration option will be available for devices with cyclic calls before and after reading inputs or outputs. It allows you to set a device-specific bus cycle task.

Per default, the parent bus cycle setting will be valid (Use parent bus cycle setting). This means that is the Devices Tree will be searched for the next valid bus cycle task definition.

To assign a specific bus cycle task, select the desired one from the selection list. The list provides the tasks currently defined in the application task configuration.