COMMUNICATION OBJECTS DESCRIPTION
Identifier
Command
Index
Subindex
Data
601h
40h
00h
20h
00h
00h
00h
00h
00h
The slave responds to the request indicating that the value of the referred object is equal to 999
:
Identifier
Command
Index
Subindex
Data
581h
4Bh
00h
20h
00h
E7h
03h
00h
00h
8.3 PROCESS DATA OBJECTS - PDOS
The PDOs are used to send and receive data used during the device operation, which must often be transmitted in
a fast and efficient manner. Therefore, they have a higher priority than the SDOs.
In the PDOs only data are transmitted in the telegram (index and sub-index are omitted), and in this way it is possible to
do a more efficient transmission, with larger volume of data in a single telegram. However it is necessary to configure
previously what is being transmitted by the PDO, so that even without the indication of the index and sub-index, it is
possible to know the content of the telegram.
There are two types of PDOs, the receive PDO and the transmit PDO. The transmit PDOs are responsible for sending
data to the network, whereas the receive PDOs remain responsible for receiving and handling these data. In this way
it is possible to have communication among slaves of the CANopen network, it is only necessary to configure one
slave to transmit information and one or more slaves to receive this information.
CANopen
Master
Transmit
PDO
Receive
PDO
Receive
PDO
Data for operation
Figure 8.2:
Communication using PDOs
✓
NOTE!
PDOs can only be transmitted or received when the device is in the operational state.
8.3.1 PDO Mapping Objects
In order to be able to be transmitted by a PDO, it is necessary that an object be mapped into this PDO content. In the
description of communication objects (1000h – 1FFFh), the filed “PDO Mapping” informs this possibility. Usually only
information necessary for the operation of the device can be mapped, such as enabling commands, device status,
reference, etc. Information on the device configuration are not accessible through PDOs, and if it is necessary to
access them one must use the SDOs.
For the manufacturer’s specific objects (2000h – 5FFFh), the table A.2 presents some PDO mapping objects. Read-
only parameters (ro) can be used only by transmit PDOs, whereas the other parameters can be used only by receive
PDOs.
1
Do not forget that for any integer type of data, the byte transfer order is from the least significant to the most significant.
SSW900 | 26