Modbus ® Specification - Tekmar 284 Integration Manual

Modbus Specifi cation
®
Communication Protocol
Physical Layer
Baud Rate
Recommended Cable
Transmission Mode
Maximum Cable Length
Start Bit
Data Length
Parity
Addressing
Modbus Connection
®
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
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conductors from the Modbus
• Gnd should not be connected to the ground screws in the 284.
A Watts Water Technologies Company
Modbus ® over RS485
RS485 two-wire plus signal ground
2400, 9600, 19200, 57600, 115000 (default: 19200 bps)
18 AWG shielded, twisted pair (STP)
RTU or ASCII (default: RTU)
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
1 bit
8 bits for RTU mode
7 bits for ASCII mode
None (2 stop bits)
Even (1 stop bit)
Odd (1 stop bit)
(default: Even)
1 to 247
(default: 1)
point to the 284 A, B & Gnd terminals.
®
8 of 12
+ –
B A
Gnd
RS 485
40 41 42
284
© 2014
B A G
(+) (-)
Master
284_B - 08/14