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BACNET INTEGRATION MANUAL FOR TB7200 & TB7300 SERIES THERMOSTATS
63-4524—01 6
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 BASRT-B repeater by Contemporary Controls can be used if a repeater is needed. 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.
Fig. 3. Correct usage – repeaters are daisy chained to the supervisory
controller and separate daisy chains branch from each repeater.
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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M32573
LEGEND
EOL: END OF LINE RESISTOR
R: RS485 REPEATER
SC: SUPERVISORY CONTROLLER
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M32574
LEGEND
EOL: END OF LINE RESISTOR
R: RS485 REPEATER
SC: SUPERVISORY CONTROLLER
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DO NOT ADD
SECOND
REPEATER
IN SERIES