Description of the CiA 402 object dictionary
Overview
This chapter contains a description of all objects.
You will find information here on:
- Functions
- Object descriptions ("Index")
- Value descriptions ("Subindices")
- Descriptions of bits
- Description of the object
Structure of the object description
The description of the object entries always has the same structure and usually consists of the following sections:
- Function
- The function of the object dictionary is briefly described in this section.
- Object description
- This table provides detailed information on the data type, preset values and similar. An exact description can be found in section "Object description"
- Value description
- This table is only available with the "Array" or "Record" data type and provides exact information about the sub-entries. A more exact description of the entries can be found in section "Value description"
- Description
- Here, more exact information on the individual bits of an entry is provided or any compositions explained. A more exact description can be found in section "Description"
Object description
The object description consists of a table that contains the following entries:
- Index
- Designates the object index in hexadecimal notation.
- Object name
- The name of the object.
- Object Code
- The type of object. This can be one of the following entries:
- VARIABLE: In this case, the object consists of only a variable that is indexed with subindex 0.
- ARRAY: These objects always consists of a subindex 0 – which specifies the number of sub-entries – and the sub-entries themselves, beginning with index 1. The data type within an array never changes, i.e., sub-entry 1 and all subsequent entries are always of the same data type.
- RECORD: These objects always consists of a subindex 0 – which specifies the number of sub-entries – and the sub-entries themselves, beginning with index 1. Unlike an ARRAY, the data type of the sub-entries can vary. This means that, e.g., sub-entry 1 may be of a different data type than sub-entry 2.
- VISIBLE_STRING: The object describes a character string coded in ASCII. The length of the string is specified in subindex 0; the individual characters are stored beginning in subindex 1. These character strings are not terminated by a null character.
- Data type
- The size and interpretation of the object is specified here. The following notation is used for the "VARIABLE" object code:
- A distinction is made between entries that are signed; these are designated with the prefix "SIGNED". For entries that are unsigned, the prefix "UNSIGNED" is used.
- The size of the variable in bits is placed before the prefix and can be 8, 16 or 32.
- Savable
- Described here is whether this object is savable and, if so, in which category.
- Firmware version
- The firmware version beginning with which the object is available is entered here.
- Change history (ChangeLog)
- Any changes to the object are noted here.
There are also the following table entries for the "VARIABLE" data type:
- Access
- The access restriction is entered here. The following restrictions are available:
- "read/write": The object can both be read as well as written
- "read only": The object can only be read from the object dictionary. It is not possible to set a value.
- PDO mapping
- Some bus systems, such as CANopen or EtherCAT, support PDO mapping. Described in this table entry is whether the object can be inserted into a mapping and, if so, into which. The following designations are available here:
- "no": The object may not be entered in a mapping.
- "TX-PDO": The object may be entered in an RX mapping.
- "RX-PDO": The object may be entered in a TX mapping.
- Allowed values
- In some cases, only certain values may be written in the object. If this is the case, these values are listed here. If there are no restrictions, the field is empty.
- Preset value
- To bring the controller to a secured state when switching on, it is necessary to preset a number of objects with values. The value that is written in the object when the controller is started is noted in this table entry.
Value description
Note:
For the sake of clarity, a number of subindices are grouped together if the entries all have the same name.
Listed in the table with the "Value description" heading are all data for sub-entries with subindex 1 or higher. The table contains the following entries:
- Subindex
- Number of the currently written sub-entry.
- Name
- Name of the sub-entry.
- Data type
- The size and interpretation of the sub-entry is specified here. The following notation always applies here:
- A distinction is made between entries that are signed; these are designated with the prefix "SIGNED". For entries that are unsigned, the prefix "UNSIGNED" is used.
- The size of the variable in bits is placed before the prefix and can be 8, 16 or 32.
- Access
- The access restriction for the sub-entry is entered here. The following restrictions are available:
- "read/write": The object can both be read as well as written
- "read only": The object can only be read from the object dictionary. It is not possible to set a value.
- PDO mapping
- Some bus systems, such as CANopen or EtherCAT, support PDO mapping. Described in this table entry is whether the sub-entry can be inserted into a mapping and, if so, into which. The following designations are available here:
- "no": The object may not be entered in a mapping.
- "TX-PDO": The object may be entered in an RX mapping.
- "RX-PDO": The object may be entered in a TX mapping.
- Allowed values
- In some cases, only certain values may be written in the sub-entry. If this is the case, these values are listed here. If there are no restrictions, the field is empty.
- Preset value
- To bring the controller to a secured state when switching on, it is necessary to preset a number of sub-entries with values. The value that is written in the sub-entry when the controller is started is noted in this table entry.
Description
This section may be present if use requires additional information. If individual bits of an object or sub-entry have different meaning, diagrams as shown in the following example are used.
Example: The object is 8 bits in size; bit 0 and bit 1 have different functions. Bits 2 and 3 are grouped into one function; the same applies for bits 4 to 7.
- Example [4]
- Description of bit 4 up to and including bit 7; these bits are logically related. The 4 in square brackets specifies the number of related bits. A list with possible values and their description is often attached at this point.
- Example [2]
- Description of bits 3 and 2; these bits are logically related. The 2 in square brackets specifies the number of related bits.
- Value 00b: The description here applies if bit 2 and bit 3 are "0".
- Value 01b: The description here applies if bit 2 is "0" and bit 3 is "1".
- Value 10b: The description here applies if bit 2 is "1" and bit 3 is "0".
- Value 11b: The description here applies if bit 2 and bit 3 are "1".
- B
- Description of bit B; no length is specified for a single bit.
- A
- Description of bit A; bits with a gray background are not used.