Honeywell TB7600 User Manual download pdf (Page 5)

BACNET INTEGRATION MANUAL FOR TB7600 SERIES THERMOSTATS

5 63-4523—02

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. TB7600 themostats' maximum data rate is 76,800 bps.

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, 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. Fig. 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. Fig. 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.

EOL

M32573

LEGEND

EOL: END OF LINE RESISTOR

R: RS485 REPEATER

SC: SUPERVISORY CONTROLLER

EOL

EOLEOL

EOL

M32574

LEGEND

EOL: END OF LINE RESISTOR

R: RS485 REPEATER

SC: SUPERVISORY CONTROLLER

EOL

DO NOT ADD

SECOND

REPEATER

IN SERIES

1 2 3 4 5 6 7 8 9 10 ... 23 24

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Honeywell TB7600 User Manual Page 5