ElmoMC CANopen DS 301 Implementation Guide - Manual (Page 42)

Chapter 8: SYNC and Time Stamp
The SYNC message has two uses:
ƒ
Synchronize the operation of synchronous PDOs. Only synchronous TPDOs can be
used to transmit data from SimplIQ digital servo drives upon receiving a SYNC
message.
ƒ Synchronize the motion clock of the servo drive with a clock in the network master.
The synchronization is made in conjunction with the Time Stamp message. The
motion clock of the servo drive counts microseconds (regardless of the sampling time
of the drive). It is cyclic and has 32 bits, meaning that it completes a full cycle in 4,295
seconds (approximately 72 minutes). When the motion clocks of all connected servo
drives are synchronized to the motion clock of the master, multiple servo drives can
perform complex synchronized motion with exact timing set by the network master.
The drives are synchronized by the transmission of a SYNC message, whose arrival time
is captured by the drive. Upon reception of the SYNC, the drive latches its internal timer.
A Time Stamp is a 32-bit message that contains the master internal clock as generated
upon receipt of the client’s own SYNC. The Time Stamp causes a clock synchronization
cycle to be executed. The drive uses the Time Stamp as an absolute timer and adjusts its
internal time in relation to the time latched in the last SYNC
1 . To synchronize the master
and drive clocks to full precision, the synchronization process is filtered in order to
ensure that the timing jitter of the time stamping process does not adversely affect
motion smoothness. It takes about 200 SYNC-Time Stamp pairs to ensure that all clocks
are fully synchronized.
COB-ID 256 (0x100) is a constant dedicated ID used for this purpose. The master can send
Time Stamps at any time.
A Time Stamp always refers to the previous SYNC message and must come no later than
5 seconds after the relevant SYNC.
1 The highest value to adjust in a single time message is 250 milliseconds.
CANopen DS 301 Implementation Guide SYNC and Time Stamp
MAN-CAN301IG (Ver. 2.1)
8-1