CANopen PDO Overview#
1. Introduction#
PDOs (Process Data Objects) are CANopen messages used for real-time data exchange between nodes. Unlike SDO (Service Data Objects), PDOs transmit data without a request/response mechanism.
2. Types of PDOs#
CANopen defines four types of PDOs per node:
PDO Type |
Direction |
CAN-ID Range |
Purpose |
|---|---|---|---|
TPDO1–4 |
Transmit PDOs |
0x180–0x1FF |
Data sent by the node to the network |
RPDO1–4 |
Receive PDOs |
0x200–0x27F |
Data received by the node from the network |
3. PDO Message Structure#
A PDO message can carry up to 8 data bytes.
Its CAN-ID and mapping are fully configurable via communication and mapping parameters.
Field |
Description |
|---|---|
CAN-ID |
Identifies which PDO it is (default values can be remapped) |
DLC |
Number of data bytes (0–8) |
Data |
Mapped application objects (e.g., sensor values, actuator commands) |
4. PDO Communication Parameters#
Each PDO has a Communication Parameter Record (object 0x1400 for RPDO1, 0x1800 for TPDO1, etc.) that defines how it is sent/received. cf: Object Dictionary
Parameter |
Description |
|---|---|
COB-ID |
The CAN-ID used for the PDO |
Transmission Type |
Defines how the PDO is triggered (synchronous, asynchronous, event-driven, cyclic) |
Inhibit Time |
Minimum time between two PDO transmissions |
Event Timer |
Periodic transmission time (in ms) |
5. PDO Mapping Parameters#
PDO mapping parameters (object 0x1600 for RPDO1, 0x1A00 for TPDO1, etc.) define which application objects are packed into the PDO data bytes.
Entry |
Description |
|---|---|
Number of Mapped Objects |
Number of data objects included in this PDO |
Mapped Object 1..n |
Each entry specifies the object index, subindex, and size in bits |
Example of a mapped TPDO1:
Byte Offset |
Mapped Object |
Description |
|---|---|---|
0–1 |
0x6041:00 (16-bit) |
Statusword |
2 |
0x6061:00 (8-bit) |
Mode of Operation Display |
6. Conclusion#
PDOs are the fast data carriers of CANopen.
They allow efficient, low-overhead communication for process data, with flexible mapping and triggering options.
✅ Use TPDOs to broadcast sensor data
✅ Use RPDOs to control actuators
✅ Configure transmission types carefully for deterministic real-time performance