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Revision 1.3 (02-11-04)
PRODUCT PREVIEW
2
SMSC TMC20073
General Description
The CircLink
ΤΜ
TMC20073 controller is an LSI device developed for DATA COMMUNICATION control
using a modified ARCNET base token passing protocol guaranteeing message integrity and maximum
delivery times which can be calculated.
In an ARCNET based network when a node receives the token it becomes the temporary master of the
network, this time frame is however, of short duration. The length of messages are limited and therefore,
no one node can dominate the network since it must relinquish control of the token. Once a message
has been sent the token is sent to the next logical node allowing it to be come the master.
By using this token passing scheme for mediating access of the network by any one node, the time
performance of the network becomes predictable or DETERMINISTIC.
Industrial network applications require predictable performance to ensure that controlled events occur
when required. The TMC20073 CircLink controller with it’s token passing protocol is therefore the ideal
solution for real time control systems.
The TMC20073 incorporates 1 kilobyte of buffer RAM which is portioned from 4 to a maximum of 32
pages. In a network which has up to 31 nodes, the data being sent by the controlling node is also
received by all other nodes of the network and stored according to node source ID. For the target node
the received data is executed per the ARCNET flow control and the data is stored in it’s buffer RAM.
Thus the receiving node acts on the data while the remaining nodes on the network discard the data
once the receiving node has executed the instruction. This redundancy assures higher reliability.
Reconfiguration of a CircLink network becomes necessary when the token is destroyed. Accordingly,
the maximum wait time for sending end will not be guaranteed during this moment and the feature of
real-time processing is impaired. To cope with the disability of real-time feature, the ARCNET protocol
is modified to avoid token missing as much as possible and reduce the network reconfiguration time in
token missing.
CircLink also uses CMI code for transmitting signals, rather than the dipulse or bipolar signals which are
the standard ARCNET signals. Since the CMI signal eliminates the DC element, a simple combination
of a standard RS485 IC and a pulse transformer can be used to implement a transformer coupled
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