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TMC2084-HD Datasheet PDF : 74 Pages
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Standalone Mode CircLink TM Controller
Datasheet
Chapter 1 General Description
1.1
About CircLink
The CircLink networking controller was developed for small control-oriented local network data
communication based on ARCNET’s token-passing protocol that guarantees message integrity and
calculatable maximum delivery times.
In a CircLink network, when a node receives the token it becomes the temporary master of the network for
a fixed, short period of time. No node can dominate the network since token control must be relinquished
when transmission is complete. Once a transmission is completed the token is passed on to the next node
(logical neighbor), allowing it to be come the master.
Because of this token passing scheme, maximum waiting time for network access can be calculated and
the time performance of the network is predictable or deterministic. Industrial network applications require
predictable performance to ensure that controlled events occur when required.
However, reconfiguration of a regular ARCNET network becomes necessary when the token is missed due
to electronic and magnetic noise. In these cases, the maximum wait time for sending datagrams can not be
guaranteed and the real-time characteristic is impaired. CircLink makes several modification to the original
ARCNET protocol (such as maximum and consecutive node ID assignment) to avoid token missing as
much as possible and reduce the network reconfiguration time.
CircLink implements other enhancements to the ARCNET protocol including a smaller-sized network ,
shorter packet size, and remote buffer mode operation that enable more efficient and reliable small,
control-oriented LANs. In addition, CircLink introduces several unique features for reducing overall system
cost while increasing system reliability.
CircLink can operate under a special mode called “Standalone” or “I/O” mode. In this mode, CircLink does
not need an administrating CPU for each node. Only one CPU is needed to manage a CircLink network
composed of several nodes, reducing cost and complexity.
In a CircLink network, the data sent by the source node is received by all other nodes in the network and
stored according to node source ID. For the target node the received data is executed per ARCNET flow
control and the data is stored in its buffer RAM. The receiving node processes the data while the remaining
nodes on the network discard the data when the receiving node has completed. This memory-mirroring
function assures higher reliability and significantly reduces network traffic.
Network Standard Time (NST) is also a unique CircLink feature. NST is realized by synchronizing the
individual local time on each network node to the clock master in the designated node from which the
packet is sent. CircLink also uses CMI code for transmitting signals, rather than the dipulse or bipolar
signals that are the standard ARCNET signals. Since CMI encoding eliminates the DC element, a simple
combination of a standard RS485 IC and a pulse transformer can be used to implement a transformer-
coupled network.
1.2
About TMC2084
The TMC2084 is CircLink’s standalone mode controller acting as an intelligent remote I/O controller that
uses the enhanced token passing protocol. TMC2084 I/O nodes are controlled by the Host node
(TMC2074/72) via the network. Thus, TMC2084 enables a single-processor with multi-remote I/O
controllers environment at reasonable cost.
SMSC TMC2084
Page 5
DATASHEET
Revision 0.1 (03-31-06)
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