C500LK009V1 Omron, C500LK009V1 Datasheet - Page 50

• Manufacturer Part Number: C500LK009V1
• Description: PC LINK UNIT
• Manufacturer: Omron

Specifications of C500LK009V1

• Leaded Process Compatible: No
• Peak Reflow Compatible (260 C): No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

SYSMAC LINK System Communications
4-1
Token Bus Communications
Polling Unit
Start-up Node
Communications Cycle
36
SYSMAC LINK System Communications
SYSMAC LINK Units communicate through the SYSMAC LINK Network, a
token bus LAN. This section describes the token bus communications used in
the SYSMAC LINK Network.
In token bus communications, individual nodes are connected to a main trunk
line as a common bus line, as shown in the figure below.
To avoid having two nodes attempt to transmit simultaneously, only one node
has the right to transmit at a time. The Unit with that right is called the pol-
ling unit. The polling unit is identified by a token that is passed in sequence
from the node to node, beginning with the node with the lowest node number.
If the token is passed to a node that doesn’t have data to transmit, the token
is immediately passed to the node with the next higher node number. The
node with the highest node number passes the token back to the node with
the lowest node number. In this way, each node in the network has its turn to
transmit data without interfering with other nodes.
In a SYSMAC LINK Network there is one node, called the polling unit, that con-
trols communications in the network. Normally, the Unit with the lowest node
number is the polling unit. If the polling unit happens to fail, the node with the next
higher node number becomes the polling unit, preventing the whole network
from failing.
The node that starts the data link in a SYSMAC LINK Network is called the
start-up node. The data link operates using the settings in the memory area
of the PC at the start-up node. With automatic allocation of link words the
settings in AR 07 are used, and with manual allocation the common link
parameters in the start-up node are used.
The start-up node controls not only data link table generation, but is used to
start and stop data link operation. Be sure to designate a Unit or Units partici-
pating in the data link as the start-up node(s) to enable this control.
The token in a SYSMAC LINK Network is first sent out from the polling unit. The
token is then is passed in sequence from the node to node by node number until
it is finally returned to the polling unit. One complete circuit around the network is
known as a token cycle.
At the end of each token cycle, the polling unit polls all of the nodes in the
network to check whether any nodes have been added to or removed from
the network. The updated information on the network is transmitted to all
nodes. This polling and updating process is known as the polling cycle.
Connecting cable
(trunk line)
Node
Node
Node
Node
Node
Highest node number
Node
Lowest node number
Node
Section 4-1