Tab ‘<device name> I/O Mapping’

Devices with I/O channels

This tab is displayed in device editors for devices with I/O channels. It shows the available channels and allows for the mapping of input, output, and memory addresses of the controller to variables of the application. In this way you create the so-called ‘I/O mapping’.

The application that is to take care of the I/O handling is defined on the PLC Settings tab.

Note

You can use the ‘online configuration mode’ if the device supports it. In this mode you can access the I/Os of the hardware without having to load a real application to the device beforehand.

Note

You can also create the I/O mapping in the dialog Edit I/O mapping. Here you get a mapping list with search and filter functions for an entire device tree.

Hint

Mapping ‘too large’ data types If a variable of a data type that is larger than a byte is mapped to a byte address, the value of the variable will be truncated to byte size there! For monitoring the variable value in the I/O Mapping dialog, this means the following: In the root element of the address, the value is displayed that the variable currently has in the project. The current individual bit values of the byte are displayed in succession in the bit elements below that, but this may not be sufficient for the entire variable value.

Example of the tab <device name> I/O Mapping for a CAN bus slave:

The tab contains a table for the editing of the I/O mapping. The information displayed for the inputs and outputs originates from the device description.

Find (1) Input field for a search string for the mapping table. The search results are marked in yellow.
Filter (2)

Drop-down list for filtering I/O mapping displayed listed in the mapping table:

  • Show all
  • Show outputs only
  • Show inputs only
  • Show unmapped variables only
  • Show mapped variables only
  • Show mappings to existing variables only
  • Show mappings to new variables only
Add FB for I/O channel (11) Available if the channel entry is selected in the mapping table, depending on the device. Opens the Select function block dialog for selecting the function block that should be linked directly to the channel.
Go to instance (12) Available if the entry is selected in the mapping table. Jumps to the corresponding entry in the <device name> IEC Objects tab.
Variable

Depending on the device, the inputs and outputs of the device are displayed as nodes and below them, indented, the associated channels or, depending on the device, only the implicitly created device instance.

The symbol indicates the type of channel:

: Input

: Output

Double-clicking the cell opens an input field.

  • Option 1: The variable already exists; specify complete path: <application name>.<module name>.<variable name>; example: app1.plc_prg.ivar; input assistance via .
  • Option 2: The variable does not exist yet; enter a simple name; automatically created internally as a global variable.

Depending on the device, inputs or outputs can be linked directly to a function block. In this case, the button Add FB for I/O channel is activated. See above.
Mapping (3)

Type of mapping:

  • : Variable already exists
  • : New variable
  • : Mapping to function block instance
Channel (4) Symbolic name of the channel.
Address (5)

Address of the channel, for example %IW0.

Address strikethrough: indicates that you should not assign any further variables to this address. Reason: Although the variable specified here – as an already existing variable – is managed at a different memory location, ambiguities could result during the writing of the values, particularly with outputs.

: Indicates that this address has been edited and fixed. If the arrangement of the device objects in the device tree changes, CODESYS does not adapt this address automatically.
Type (6)

Data type of the channel, for example BOOL.

Structures or bit fields defined in the device description are displayed only if they are part of the IEC standard and are identified as IEC data types in the device description. Otherwise the table cell remains empty.

When mapping structured variables, the editor prevents you from entering both the structure variable (example: %QB0) and individual structure elements (example: %QB0.1 and QB0.2). Therefore, if there is a main entry with a subtree of bit channel entries in the mapping table, then the following applies: You can input a variable either into the line of the main entry, or into the lines of the subelements (bit channels), but not into both.
Default value

Default value of the parameter that applies to the channel: Appears only if the option Set all outputs to default value is activated in the PLC Settings for the behavior of the outputs at stop.

Note: For compiler version V3.5 SP11 and later, the initialization value of the variables is used automatically as the default value when mapping to an existing variable. You can edit the Default value field only if you map to a new created variable or if no mapping is specified. In older versions, users had to specify explicitly that the default value and initialization value were identical.
Unit (7) Unit for the parameter value, for example ms for milliseconds.
Description (8) Brief description of the parameter.
Current value Actual value of the parameter applied to the channel; displayed in online mode only.
Reset mapping (9) CODESYS resets the mapping settings to the default values defined by the device description file.
Update variables (10)

Definition for the device object about updating I/O variables. The default value is defined in the device description:

  • Use settings from the superordinate device: Update according to the setting of the superordinate device.
  • Activates 1 (use bus cycle task if not used in another task): CODESYS updates the I/O variables in the bus cycle task if they are not used in any other task.
  • Activate 2 (always in bus cycle task): CODESYS updates all variables in each cycle of the bus cycle task, regardless of whether they are used and whether they are mapped to an input or output channel.

Note

If a UNION is represented by I/O channels in the mapping dialog, it depends on the device whether mapping to the root element is also possible.

Devices with I/O drivers

For devices with I/O drivers, you can set the bus cycle task here in the I/O Mapping tab if the general settings should not be used (PLC Settings tab).

Bus cycle options
Bus cycle task The drop-down list provides all tasks that are defined in the task configuration of the active application (example: MainTask). In case of Use parent bus cycle setting, the settings of the parent node will be used.

General information about the bus cycle task

As a rule, for each IEC task the used input data is read at the start of each task (1) and the written output data is transferred to the I/O driver at the end of the task (3). The implementation in the I/O driver is decisive for further transfer of the I/O data. It is responsible for the time frame and time point that the actual transfer to the corresponding bus system occurs.

The bus cycle task of the PLC can be defined globally for all fieldbuses in the PLC settings. For some fieldbuses, however, you can change this independent of the global setting. The task with the shortest cycle time is used as the bus cycle task (setting: unspecified in the PLC settings). The messages are normally sent on the bus in this task.

Other tasks copy only the I/O data from an internal buffer that is exchanged only with the physical hardware in the bus cycle task.

(1) Read inputs from input buffer             (2) IEC task
(3) Write outputs to output buffer      (4) Bus cycle
(5) Input buffer                                    (6) Output buffer
(7) Copy data to/from bus
(9) Bus cycle task, priority 1, 1 ms
(10) Bus cycle task, priority 5
(11) Bus cycle task, priority 10, interrupted by task 5

Task usage

The Task deployment provides an overview of used I/O channels, the set bus cycle task, and the usage of channels.

Warning

If an output is written in various tasks, then the status is undefined, as this can be overwritten in each case.

If the same inputs are used in various tasks, it is possible for the input to change during the processing of a task. This happens if the task is interrupted by a task with a higher priority and causes the process map to be read again. Solution: At the beginning of the IEC task, copy the input variables to variables and then work only with the local variables in the rest of the code.

Conclusion: Using the same inputs and outputs in several tasks does not make any sense and can lead to unexpected reactions in some cases.

See also