YASKAWA SGMSS - Introduction; Overview; Synqnet Packet Timing

6 SynqNet™ Communications
6.1.1 Overview
6-2
6.1 Introduction
6.1.1 Overview
SynqNet™ is a synchronous network technology designed for multi-axis motion control applications. The physi-
cal layer of SynqNet is based on the physical layer of Ethernet. SynqNet operates over two pairs of wires, one
pair for 'receive' data signals and the other pair for 'transmit' data signals. Each receiving node uses digital time-
correction techniques to minimize skew and jitter. Service channel capability is used to query nodes or servo for
drive parameters and status information.
6.1.2 SynqNet Packet Timing
SynqNet is unlike other synchronous digital servo network protocols in the way that command and response mes-
sages are handled. With other servo networks, the cyclic and service channel commands and responses are usu-
ally handled in a single data packet per controller cycle. In SynqNet, the cyclic data demands, cyclic data
responses, service channel demands, and service channel responses may occur in separate communication buff-
ers during the controller cycle. This is implemented by utilizing a drive update period (drive cycle) that is faster
than the controller cycle. The communications buffer is checked by the drive every drive cycle. An integral num-
ber of drive cycles must make up one controller cycle.
In other servo networks, the data packet size and node time slots are usually fixed. This is neither true with Syn-
qNet nor PROFIBUS. During startup network configuration, the SynqNet controller determines when in each
controller cycle the individual nodes will receive new demands and when the responses will be read. The resolu-
tion of the SynqNet node communication scheduling is 40 nanoseconds. Each node may have a different packet
size depending on the number of axes supported.
During every SynqNet controller cycle every axis in every node will receive a new cyclic demand. All drives are
notified of new cyclic data at the same time via a strobe mechanism.
During a SynqNet controller cycle there may be one service channel request per node. Since a node may have
multiple axes, it is not possible to handle service channel requests for multiple axes at the same node during the
same controller cycle. The service channel request may not occur during the same drive cycle as the cyclic
demand.
The main advantage of this architecture is that the time from controller update until drive update is minimized.
Also, the time from drive position update to new controller update is also minimized.
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