MAGS1 User Guide
7
V1.5 22-1-2016
3. RS485 communication
The only way to set and read the flowmeter is via RS485 interface, the communication protocol is Modbus
RTU over serial port, RS485 is standard for sending serial data, it uses a twisted pair of wires to send a
differential signal over distances up to 1200 m without a repeater.
The differential signal makes it very robust, RS485 is one of the most popular communications methods
used in ind
ustrial applications where it’s noise immunity and long-distance capability are a perfect fit.
RS485 is capable of multi-drop communications
– up to 32 nodes.
In the following picture, the general network topology of RS485 is shown. N nodes are connected in a
multipoint RS485 network, for longer lines, the termination resistances Rt are necessary on both ends of
the line to eliminate reflections, use 100
Ω resistors on both ends.
The RS485 network must be designed as one line with multiple drops, not as a star.
Although total cable length maybe shorter in a star configuration, adequate termination is not possible
anymore and signal quality may degrade significantly.
Electrical Specifications
Maximum voltage
- 7 V up to + 12 V at bus terminal A or B (separately or common mode)
Baudrate
9600, 14400, 19200, 38400, 57600, 115200
Parity
no parity, Odd parity, Even parity, No parity 2 stopbits
Max distance
up to 1200m depends on cable parameters
Cabling requirements
twisted pair, plus signal ground for long distances
Multidrop
up to 32 nodes
Operating temperature
0
– 70 °C
