Tekmar 284 - Modbus Specification

© 2014 284_B - 08/14
8 of 12
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
BAG
Master
284
40 41 42
Gnd
+–
RS 485
BA
(+)
(-)
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.•