TMC2074-NE SMSC, TMC2074-NE Datasheet - Page 6

• Manufacturer Part Number: TMC2074-NE
• Description: Network Controller & Processor ICs Standalone Mode CircLink Cntlr
• Manufacturer: SMSC

Specifications of TMC2074-NE

• Product: Controller Area Network (CAN)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Chapter 1
1.1
Revision 0.2 (10-23-08)
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.
General Description
DATASHEET
Page 6
Dual Mode CircLink™ Controller
SMSC TMC2074
Datasheet