TMC2072-MD SMSC, TMC2072-MD Datasheet - Page 27

• Manufacturer Part Number: TMC2072-MD
• Description: Network Controller & Processor ICs Peripheral Mode CircLink Cntlr
• Manufacturer: SMSC

Specifications of TMC2072-MD

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

Peripheral Mode CircLink™ Controller
Datasheet
2.4
2.4.1
2.4.2
NOTE:
SMSC TMC2072
CircLink Protocol Enhancement
Since the communication of ARCNET is controlled by a token, a token loss and the corresponding
reconfiguration significantly reduce the throughput of the network. In order to maintain the throughput,
modification of the ARCNET protocol is required to realize even higher real-time performance.
Reducing Token Loss
The primary source of token loss is caused by the burst signal. The burst signal is part of the sequence for
new nodes joining the network as described in section 2.3. In the CircLink, however, any new nodes do not
join because all nodes join to the network at the system start-up. In exceptional cases, the node leaves the
network due to token loss and a burst signal sent to r re-join the network. In order to avoid this burst signal,
the ARCNET protocol has been modified to specify node IDs as consecutive numbers starting from 01.
When a node other than the node having the largest node ID (NID [4:0] and MAXID[4:0]) sends a token
with the starting address being the node ID +1, this avoids sending a burst because a token can be
received in the next polling, even if a node has accidentally dropped out from the network.
The token retry function has been added to CircLink such that the possibility of not receiving the response
from the logical neighbor is greatly reduced due to token corruption . . Since the node ID in the CircLink is
consecutive and the retry does not occur in normal conditions, the token retry function does not degrade
the total performance. This function can be set to ON or OFF using software settings. (The default is ON)
Another cause of the token loss is the corruption of ACK/NAK. In the ARCNET flow (refer to page 12 in the
ARCNET controller COM20020I datasheet), if the node receives other signals other than the anticipated
ACK/NAK response (such as noise or, data-deformed ACK/NAK and the like), this node returns to the
receive-wait state with a token being held by the node. The network considers this as a token loss because
the token disappears from the network. To avoid this problem, ARCNET protocol has been modified to
send a token even after the detection of ACK/NAK corruption This function against the ACK/NAK
deformation can be set to ON or OFF. (The default is ON.)
Reduction of Network Reconfiguration Time
To reduce the waiting duration of (255 - ID) x 146 μs* during the network reconfiguration time, CircLink
designates a the node with the maximum ID as the maximum node (MAX_NODE). The node designated to
the maximum node immediately starts sending a token. The destination number starts from 00. The token
sending to 00 is not received by any node but triggers the other nodes to enter into the receive state out of
the (255 - ID) x 146 μs* timer. In addition, the 255 of (255 - ID) x 146 μs* timer formula, derived from
ARCNET, the is modified to
(The maximum number of nodes –ID) x 146 μs depending on the maximum number of nodes, which is
specified by the MAXID [4:0] pin. This modification makes significant reduction of the time required for
network reconfiguration even in the absence of the node set as MAX_NODE.
* 146 μs is the time under operation at 2.5 Mbps. The time is half at 5 Mbps..
DATASHEET
Page 27
Revision 0.1 (06-07-07)