Communication Objects - Cob; Cob-Id - WEG CFW-11 Communications Manual

1.7 Communication Objects - COB

There is a specific set of objects that are responsible for the communication among the network devices. Those
objects are divided according to the type of data and the way they are sent or received by a device. The CFW-11
supports the following communication objects (COB):
Type of object
Service Data Object
SDO are objects responsible for the direct access to the object dictionary of a device. By means of messages using SDO, it
(SDO) is possible to indicate explicitly (by the object index) what data is being handled. There are two SDO types: Client SDO,
responsible for doing a read or write request to a network device, and the Server SDO, responsible for taking care of that
request. Since SDO are usually used for the configuration of a network node, they have less priority than other types of
message. Only a Server SDO is available for the CFW-11.
Process Data Object
PDO are used for accessing equipment data without the need of indicating explicitly which dictionary object is being
(PDO) accessed. Therefore, it is necessary to configure previously which data the PDO will be transmitting (data mapping). There
are also two types of PDO: Receive PDO and Transmit PDO. They are usually utilized for transmission and reception of
data used in the device operation, and for that reason they have higher priority than the SDO.
Emergency Object This object is responsible for sending messages to indicate the occurrence of errors in the device. When an error occurs in a
(EMCY) specific device (EMCY producer), it can send a message to the network. In the case that any network device be monitoring
that message (EMCY consumer), it can be programmed so that an action be taken (disabling the other devices, error reset,
etc.). The CFW-11 has only the EMCY producer functionality.
Synchronization Object
In the CANopen network, it is possible to program a device (SYNC producer) to send periodically a synchronization
(SYNC) message for all the network devices. Those devices (SYNC consumers) will then be able, for instance, to send a certain
datum that needs to be made available periodically. The CFW-11 has the SYNC consumer function.
Network Management
Every CANopen network needs a master that controls the other devices (slaves) in the network. This master will be
(NMT) responsible for a set of services that control the slave communications and their state in the CANopen network. The slaves
are responsible for receiving the commands sent by the master and for executing the requested actions. The CFW-11
operates as a CANopen network slave and makes available two types of service that the master can use: device control
service, with which the master controls the state of each network slave, and error control service (Node Guarding), with
which the slave sends periodic messages to the master informing that the connection is active.
All the communication of the inverter with the network is performed using those objects, and the data that can be
accessed are the existent in the device object dictionary. The working description of each COB is presented in
section 7.

1.8 COB-ID

A telegram of the CANopen network is always transmitted by a communication object (COB). Every COB has an
identifier that indicates the type of data that is being transported. This identifier, called COB-ID has an 11 bit size,
and it is transmitted in the identifier field of a CAN telegram. It can be subdivided in two parts:
Function Code: indicates the type of object that is being transmitted.
Node Address: indicates with which network device the telegram is linked.
A table with the standard values for the different communication objects available in the CFW-11 is presented next.
Notice that the standard value of the object depends on the slave address, with the exception of the COB-ID for
NMT and SYNC, which are common for all the network elements. Those values can also be changed during the
device configuration stage.
Table 1.1 - Types of Communication Objects (COB)
Function Code
bit 10 bit 9 bit 8 bit 7
Table 1.2 - COB-ID for the different objects
COB
NMT
SYNC
EMCY
PDO1 (tx)
PDO1 (rx)
PDO2 (tx)
PDO2 (rx)
PDO3 (tx)
PDO3 (rx)
PDO4 (tx)
PDO4 (rx)
SDO (tx)
SDO (rx)
Node Guarding/Heartbeat
Description
Node Address
bit 6 bit 5 bit 4 bit 3
Function code
(bits 10 – 7) (function + address)
0000
0001
0001 129 – 255 (81h – FFh)
0011 385 – 511 (181h – 1FFh)
0100 513 – 639 (201h – 27Fh)
0101 641 – 767 (281h – 2FFh)
0110 769 – 895 (301h – 37Fh)
0111 897 – 1023 (381h – 3FFh)
1000 1025 – 1151 (401h – 47Fh)
1001 1153 – 1279 (481h – 4FFh)
1010 1281 – 1407 (501h – 57Fh)
1011 1409 – 1535 (581h – 5FFh)
1100 1537 – 1663 (601h – 67Fh)
1110 1793 – 1919 (701h – 77Fh)
bit 2 bit 1 bit 0
Resultant COB-ID
0
128 (80h)