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ARCNET 5 Port HUB Controller
Datasheet
SMSC TMC2005-JT Page 23 Revision 1.1 (07-24-07)
DATASHEET
CASCADING CONNECTION
HUBs can be connected in cascade by using the ports as Fig. 12. In the case of cascade connection, it is necessary
to consider how many HUBs can exist in serial. The maximum delay between input port and output port is 650ns
@2.5Mbps at the TMC2005. It is equivalent to the propagation delay when a cable length is 135m. For example, if
every cable length is 10m in Figure 12, the longest distance is physically 50m but it is electrically 590m because of
multiplying 10m by 5 and 135m by 4, and the total propagation delay becomes 2.8uS. For analyzing the network
timing, consider the delay caused by HUBs. In the ARCNET protocol, it is defined that the longest distance between
nodes is the maximum 6.4Km. For example, if 20 TMC2005s exist between nodes in the longest distance, the actual
cable length is 3.7Km because of deducting 135m by 20 in converting to cable length from 6.4Km.
FIGURE 12 - CASCADE CONNECTION OF 4 HUBS
Two examples of eight ports HUBs using two TMC2005s are shown in Fig. 13 and 14. If connecting as in Fig. 13,
eight TMC2005s exist between the nodes at both far ends. On the other hand, when assigning two ports for
cascading connection to the same TMC2005, the number of TMC2005 in serial connection can be down to the
number of HUBs plus two, which can reduce the propagation delay.
TMC2005
5
4
3
2
1
Port 5
Port 4
Port 3
Port 2
Port 1
TMC2005
5
4
3
2
1
Port 5
Port 4
Port 3
Port 2
Port 1
TMC2005
5
4
3
2
1
Port 5
Port 4
Port 3
Port 2
Port 1
TMC2005
5
4
3
2
1
Port 5
Port 4
Port 3
Port 2
Port 1
NODE NODE