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7-15
Chapter 7: Computer Link Function
7
[8] Cyclic transfer and data area
(1) Outline of the cyclic transfer process
The cyclic transfer process is a function that supports cyclic data exchanges that occur between
nodes.
1 Establishes the common memory function.
2 Transmits when a node receives the token.
3 Nodes which do not execute cyclic transfers within the network are allowed to participate.
4 When received the token, the node sends all the cyclic data that it needs to send.
- Token: Generally, only one token exists in a network. If more than one token exists in a
network, the token with the lowest destination node number has priority and any other token
is discarded.
- Token frame: A frame with a token has a destination node number and a transmitting node
number. The node whose number matches the destination node number holding the token.
- Token order: The token rotation order is determined by the node numbers. The token is
passed to the nodes in order that the nodes were registered in the participating node man-
agement table. The node with the highest node number hands the token over to the node
with the lowest node number.
Token rotation and cyclic transfer 1
Token rotation and cyclic transfer 2
Time
Node #1
Token
Node #2 Node #3 Node #N
Node #1
Token
Node #2 Node #3 Node #N
Time
Node #1
Token
Node #2
Node #N-1
Node #N
Node #1
Token
Node #2
Node #N-1
Node #N