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TPDO Communication Parameters


The Index area from 1800h to 19FFh in the Object Dictionary is reserved for the TPDO communication parameters. As with the RPDOs, the Index range ensures that a maximum of 512 TPDOs can be configured for a single CANOPEN node. The parameters for the first TPDO (TPDO1) are located at Index 1800h, the parameters for the second at 1801h (TPDO2), for the third at 1802h (TPDO3) and so on.

The parameters for each TPDO are accessible via the Subindex. The table below shows the parameters that are available for every TPDO.

SubindexNameData type
0Number of entriesUNSIGNED8
1COB-IDUNSIGNED32
2Transmission typeUNSIGNED8
3Inhibit TimeUNSIGNED16
4ReservedUNSIGNED8
5Event TimerUNSIGNED16

The Number of entries for a TPDO is 5, as five parameters are available for the configuration of each TPDO. Only entries zero through two are mandatory, three and five are optional.

As with the RPDO, the COB ID specifies the CAN message identifier used when transmitting this TPDO. For more information see COB ID and CAN ID partitioning.

The transmission type selects the TPDO trigger behavior. The following table lists the available transmission types for a Transmit PDO:

Transmission TypeDescription
0The Transmit PDO is synchronous. Which specific SYNC Object occurrence triggers the transmission is given in the device profile. Additional details of the PDO transmission are given in the device profile.
1 – 240The Transmit PDO is synchronous. It is transmitted after every nth SYNC Object within the Synchronous Window Length, where n is the transmission type. For example, when using transmission type 34, the PDO is transmitted after every 34th SYNC Object.
241 – 251Not used for Transmit PDOs
252The data for the PDO is updated on reception of a SYNC Object, but the PDO is not transmitted. The PDO is only transmitted on reception of a Remote Transmission Request.
253The data for the PDO is updated and the PDO is transmitted on reception of a Remote Transmission Request.
254The conditions that cause the Transmit PDO to be transmitted are manufacturer specific.
255The Transmit PDO is asynchronous. Details of when the PDO is transmitted is given in the device profile.

Subindex 03h is optional and defines the inhibit time for the PDO. The inhibit time specifies the minimum time between transmissions of the PDO. Once the PDO is transmitted, any additional transmissions of the PDO will not take place during the inhibit time.

This minimum timeout between two transmissions of a TPDO are specified in multiples of 100 microseconds. Note that the inhibit time is measured from the time when the node first attempts to send the PDO. If the PDO is blocked from being sent because of higher priority messages on the bus, then the delay before the PDO is actually transmitted is included in the inhibit time. Therefore the inhibit time must be greater than the worst case transmission time of the PDO.

The Reserved parameter is a legacy value from previous CANOPEN versions and must not be implemented in nodes conforming to the current standard [CiADS302].

For event time driven TPDOs the Event Time specifies the time period used for this TPDO. The Event Time is specified in multiples of milliseconds. If it is set to 100 the TPDO is transmitted every 100 milliseconds. Using a combination of both Inhibit Time and Event Time creates a time window for the transmission of the TPDO. It will be transmitted at least every "Event Time" but not more often then defined by the "Inhibit Time". Each time the PDO is transmitted as a result of the event timer expiring, the event timer is reset.

One of the advanced features of CANOPEN is that it supports all generally known transmission and communication methods used in communication networks. CANOPEN nodes can not only transmit their data individually (either event or time driven) they can also be polled individually or synchronized in groups. In addition, any of these methods can be combined. For further info see Network Synchronization.