BAS Integration Manual

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A Watts Water Technologies Company

Communication Protocol Modbus

over RS485

Physical Layer RS485 two-wire plus signal ground

Baud Rate 2400, 9600, 19200, 57600, 115000 (default: 19200 bps)

Recommended Cable 18 AWG shielded, twisted pair (STP)

Transmission Mode RTU or ASCII (default: RTU)

Maximum Cable Length 11500 bps: 580 ft (177 m)

57600 bps: 1,158 ft (353 m)

19200, 9600, 2400 bps: 3,280 ft (1,000 m)

3,280 ft (1,000 m) for all baud rates if 120 Ohm terminating resistors used

Start Bit 1 bit

Data Length 8 bits for RTU mode

7 bits for ASCII mode

Parity None (2 stop bits)

Even (1 stop bit)

Odd (1 stop bit)

(default: Even)

Addressing 1 to 247

(default: 1)

Modbus

Speciﬁ cation

Modbus

Connection

ABG

Master

284

40 41

Modbus

Gnd

Use a top or back knock-out to bring a shielded twisted pair wire from the nearest

Modbus

RS485 connection point into the wiring chamber. Wire the A, B & G

conductors from the Modbus

point to the 284 A, B & Gnd terminals.

Gnd should not be connected to the ground screws in the 284.•