Trane BAS-APG001-EN manual Communication watchdog, Programming

Chapter 7 Programming

Communication watchdog

Since multiple Tracer MP581s are used to interface with the mechanical equipment and FACP and FSCS panels, checking communications between each MP581 and BCU is necessary. Three different communication systems are used: BCU to MP581 (auto-bind), MP581 to MP581 (custom bind), and MP581 to EX2. The BCU cannot determine communication status of custom bindings.

One Tracer MP581 should be chosen to be the communication watchdog. Otherwise, the number of watchdog timers and Tracer MP581 permutations may exceed binding limits.

Figure 62 on page 113 illustrates the communication watchdog relationship. Figure 63 and Figure 64 on page 113 are TGP examples of the transmitting and receiving units, respectively. From the point of view of the receiving MP581, this technique tests whether the central unit can transmit by u sing a custom binding. As long as the programmer chooses to test from both ends, this process will fully test the communication status of the MP581-to-MP581 system. Other communication status such as that of the I/O bus (EX2 modules) and BMTX BCU can also be transferred to the central MP581.

The basic watchdog method consists of sending an alternating signal from one MP581 to another MP581. A custom binding is necessary for the MP581-to-MP581 communication link. Although there are many ways to bind the two devices, for this example use MP581-2/nvoswitch36 to MP581-1/nviSwitch38. Whenever nviSwitch38 goes from false to true, a retriggerable latch block is triggered, holding its output state to true When a number of stat changes are missed—typically three—an alarm event will be triggered at the BCU. It may be necessary to adjust the delay time of the latch block to avoid false communication alarms.

A response to communication status is necessary only if communication fails at any level. According to UL, a mechanical system reaction to communication loss is not necessary. Local requirements may require a mechanical reaction to communication loss.

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