Process data transfer
Process data objects (PDOs) are used for the cyclic transmission of (process) data via CANopen.
PDOs only contain data and an identifier. They do not contain any information about the sender or receiver and are therefore very efficient.
Details
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Process data objects which the inverter receives via the network are referred to as "Receive PDOs" (RPDOs).
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Process data objects which the inverter sends via the network are referred to as "Transmit PDOs" (TPDOs).
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The maximum length of a PDO is 8 bytes (4 data words).
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Each PDO requires a unique identifier ("COB-ID") for the purpose of identification within the network.
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Communication parameters such as the transmission type and cycle time for each
PDO can be set freely and independently of the settings of other PDOs
Transmission type
Process data objects can be transmitted in an event-controlled or time-controlled manner.
The below table shows that it is possible to combine the different methods by means of
logic operations (AND, OR):
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Event-controlled:
The PDO is sent if a special device-internal event has occurred, for instance, if the data contents of the TPDO have changed
or if a transmission cycle time has elapsed.
–
Synchronous transmission:
Transmission of a TPDOs or reception of an RPDO is effected after the inverter has received
a sync telegram (COB-ID 0x80).
–
Cyclic transmission:
The cyclic transmission of PDOs is effected when the transmission cycle time has elapsed.
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Polled via RTR:
Transmission of a TPDO is carried out on request by another device via data request frame
(RTR remote transmit request). For this, the data requester (e.g. master)
sends the data request frame with the COB-ID of the TPDO that is to be requested
to transmit. The receiver recognises the RTR and carries out the transmission.
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Transmission type
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PDO transmission
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Logic combination of different transmission types
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cyclic
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synchronous
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event-controlled
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0
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l
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l
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AND
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1 ... 240
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l
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-
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254, 255
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l
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l
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OR
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Transmission type
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Description
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0
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Synchronous and acyclic
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The PDO is transmitted on an event-controlled basis with every sync (e.g. when a bit change
occurs in the PDO).
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1 ... 240
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Synchronous and cyclic (sync-controlled with a response)
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Selection n = 1: The PDO is transmitted with every sync.
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Selection 1 < n ≤ 240: The PDO is transmitted with every n-th sync.
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241 ... 251
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Reserved
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252
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Synchronous - RTR only
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253
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Asynchronous - RTR only
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254, 255
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Asynchronous - manufacturer-specific / device profile-specific
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If the value 255 is entered, sending and receiving takes place in the set cycle time. Linked signals are also sent and received every time the PDO is changed. The PDO is event-driven and cyclically transmitted.
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If the value 254 is entered, sending and receiving takes place in the set cycle time. A change in the PDO linked signals has no influence.
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Synchronisation of PDOs via sync telegram
During cyclic transmission, one or more PDOs are transmitted/received in fixed time intervals.
An additional specific telegram, the so-called sync telegram, is used
for synchronising cyclic process data.
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The sync telegram is the trigger point for the transmission of process data from the slaves to
the master and for the acceptance of process data from the master in the slaves.
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For sync-controlled process data processing, the sync telegram must be generated
accordingly.
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The response to a sync telegram is determined by the transmission type selected.
Generating the sync telegram:
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0x1005 can be used to activate the generation of sync telegrams and to write
the identifier value.
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Sync telegrams are created when bit 30 (see below) is set to "1".
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The
interval between sync telegrams is to be set in 0x1006.
Writing identifiers:
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To receive sync telegrams, the value 0x80 must be entered in the 11-bit
identifier in the default setting (and in compliance with the CANopen specification). This means
that all inverters are set to the same sync telegram by default.
–
If sync telegrams are only to be received by specific nodes,
their identifiers can be entered with a value of up to and including 0x07FF.
–
The identifier can only be changed if the inverter does not
send any sync telegrams (0x1005, Bit 30 = "0").
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8th byte (data 4)
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7th byte (data 3)
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6th byte (data 2)
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5th byte (data 1)
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Bit 31
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Bit 30
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Bit 29 ... bit 11
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Bit 10 ... bit 0
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x
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0/1
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Extended identifier*
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11-bit identifier
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* The extended identifier is not supported. Bit 11 ... bit 29 must be set to "0".
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Parameter