Honeywell TB7200 Integration Manual page 6

BACNET INTEGRATION MANUAL FOR TB7200 & TB7300 SERIES THERMOSTATS
Maximum Cable Length
The maximum length of a chain is related to its transmission speed. The longer the chain, the slower the speed. Using proper
cable, the maximum length of an EIA-485 daisy chain is 4000-ft (1200 m). This will only work reliably for data rates up to 100,000
bps. The maximum data rate is 76,800 bps for TB7200 and TB7300 Series thermostats.
If you require a maximum network length of more than 4000 feet, then repeaters are required to extend the network.
EIA-485 Repeaters
If you have more than 64 devices, or require a maximum network length of more than 4000 feet, then repeaters are required to
extend the network. The best configuration is to daisy chain the repeaters to the controller. From each of these repeaters, a
separate daisy chain will branch off. Figure 3 demonstrates a valid use of repeaters in an EIA-485 network.
Do not install repeaters in series, as this may result in network reliability problems. Figure 4 demonstrates an incorrect use of a
repeater in an EIA-485 network.
Fig. 4. Incorrect usage – the second repeater in series may result in an unreliable system.
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Fig. 3. Correct usage – repeaters are daisy chained to the supervisory
controller and separate daisy chains branch from each repeater.
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DO NOT ADD
SECOND
REPEATER
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IN SERIES
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R: RS485 REPEATER
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R: RS485 REPEATER
SC: SUPERVISORY CONTROLLER
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