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TMC2074

Dual Mode CircLink™ Controller

SMSC -> Microchip 

Chapter 1 General Description

Dual Mode CircLink™ Controller

Datasheet

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 cycle time.

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. Control networking 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 cannot 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 up to maximum 31 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.

Revision 0.1 (03-29-06)

Page 6

DATASHEET

SMSC TMC2074

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