SMSC TMC2005-JT - Manual (Page 26)

ARCNET 5 Port HUB Controller
Datasheet
Revision 1.1 (07-24-07) Page 26 SMSC TMC2005-JT
DATASHEET
Ring Network With the TMC2005
The reliability of the network can be improved by connecting every node in a ring, because the communication is
maintained through the reverse route even if the cable is cut at a point. However ARCNET controller alone can not
support ring, because ARCNET is a half-duplex communication system. Using HUBs makes possible for ARCNET to
built a ring network as in Fig.16. This configuration is available only for using fiber optics. (Refer to the application note
for details.)
FIGURE 16 - RING CONFIGURATION
Note 1:
Noise may cause an endless loop in a ring system, and the network may hang up. Therefore take care of
designing the patterns between TMC2005 and transceiver or cabling of system.
Example for system hang-up
- A noise occurs only at “A” point in Figure 16.
- The noise propagates clockwise on the network.
- TMC2005 detects the noise that came back through the ring.
- The noise causes an endless loop in the ring.
Example for no hang-up
- Any noise occurs at “A” and “B” points in Figure 16 at the same time.
- The noise propagates to both directions in the network.
- An endless loop doesn’t occur because TMC2005s in the middle absorb the noise from both sides.
Note 2: Place a watch dog timer on one of the TMC2005 in at least one ring. To protect from hang-up the detecting
time of the watch dog timer should be set to longer than 2.7 mS (@ 2.5Mbps) that is the burst time in the
ARCNET protocol.
Note 3:
Consider that a total of each segment delay time (cable delay, TMC2005 delay, driver delay and receiver
delay) between HUBs in a network is less than 5.6uS (@ 2.5Mbps). The maxmimum distance between
HUBs is approximiately 1000m (@ 2.5Mbps).
TMC2005
COM20020
nRESET
CK CT
TMC2005 COM20020
TMC2005
COM20020
TMC2005 COM20020
Optical Fiber
A
B
Optical Transceiver
TXEN of any port
TXEN
nRST