User Manual Of EL7-EC** AC Servo
258
7.4.2 Object dictionary
EtherCAT master controls the EL7-EC drive by writing and reading device state
/information. To do this, the drive defines read-write parameters and read-only state
values. Object dictionary is the collection of these parameters and states.
The EL7-EC object dictionary contains all DSP402 and CoE related data objects in a
standardized manner. It is a collection of EL7-EC parameter data structures.
The EL7-EC object dictionary is the interface with which the controller communicates.
EtherCAT master implements EL7-EC motion control through the interface of object
dictionary.
7.4.3 Service Data Object (SDO)
The EL7-EC series supports SDO services. EtherCAT master can configure, monitor and
control EL7-EC servos by using SDO to read and write EL7-EC object dictionaries.
In conventional CANopen DS301 mode, SDO protocol CAN only transfer 8 bytes at a time
to match the data length of CAN message. In COE enhancement mode, only the payload
data is expanded without changing the protocol head; In this way, the SDO protocol uses
mailboxes with larger data lengths, thus improving the transmission efficiency of big
data.
7.4.4 Process Data Object (PDO)
PDO Introduction
PDO is generally used for real-time data updates. It is divided into receiving PDO (RXPDO)
and sending PDO (TXPDO). The data stream direction of receiving PDO is from master
station to slave station, while sending PDO is from slave station to master station
The PDO function of EL7-EC supports both synchronous cycle mode and non-periodic
update mode. When distributed clock synchronization mode is selected on master
station, PDO will update according to the synchronization cycle. If free moving mode is
selected, PDO data updates aperiodic.
PDO mapping
Through PDO mapping, the real-time transmission of mapped objects can be realized.
EL7-EC supports simultaneous transmission of 2 sets of RXPDO and 2 sets of TXPDO.
Each PDO object can map up to 8 object dictionary (maximum length 32 bytes). The
format of PDO mapping content is shown in table 6.2
Table 7.2 Format of PDO mapping
Bit
31~16
15~8
7~0
Description
Index of mapped
object
Subindex of mapped
object
Bit length
(Hex)
Example
6040h
00h
10h(16bit)
