BAS-SVX51L-EN 33
Trane SerialSpy Protocol Analyzer Software
Gaps in Rotary Switch Addressing
BACnet
®
devices use a set of token-passing rules that allow them to get organized within seconds of
power-up. Figure 22, p. 33 shows token-passing and data requests on a clean link. Note that there is a
gap between address 3 and address 49. The device at address 3 will poll each time it has the token. Each
time it polls it will look for the next highest address. You can see the fist poll for address 37, the next for
38 and so on. Polling results in an unnecessary additional message on the link, which will reduce
performance. For this reason, Trane recommends that addresses be set up sequentially when possible.
Note: Once the device has polled the last address in the gap, it will stop polling for new devices for the
next 50 token cycles. After 50 cycles, it will try each address again.
Figure 22. Device 3 polling
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