Navigator 540 | Transmitter |
COM/AWT540/PB–EN Rev. C
13
5 Modbus communications
This section describes the connection of serial data cables
between the master (host computer) and slave (Navigator
AWT540 transmitter) on a Modbus serial link.
5.1 Host computer serial communications
The serial interface option module operates using the Modbus
Remote Terminal Unit (RTU) Master / Slave protocol. An
appropriate RS422 / 485 communications driver must fitted to
the host (master) computer. It is strongly recommended that
the interface has galvanic isolation to protect the computer
from lightning damage and to increase signal immunity to noise
pick-up.
IMPORTANT (NOTE)
Modbus menus are enabled only if a Modbus
communications module is fitted.
Menu
Comment
Default
MODBUS
Device Address
Set a device-specific address (from 1 to
247) to identify the transmitter on a
Modbus link.
RS485 Setup
Mode
Select the Modbus serial communication
serial link type:
2 Wire
,
4 Wire
or
Off
4 Wire
Baud Rate
Select a communication transfer rate:
1200
,
2400
,
4800
,
9600
,
19200
,
38400
or
115200
baud.
19200
Parity
Select the parity bit (transmission
error-checking) condition:
No Parity
,
Odd Parity
or
Even Parity
No Parity
Tx Delay
Set a delay to the response from the
transmitter in milliseconds. Maximum
delay 100 ms.
50 ms
IMPORTANT (NOTE)
The Modbus option provides the following facilities:
— Standard RS422/485 communications.
— Modbus RTU protocol – the transmitter is designed
to operate as a Remote Terminal Unit (RTU) slave
when communicating with a master (host) system.
— 500V DC isolation from external connections to the
instrument.
— Two- or four-wire communication (selected at the
RS485 Setup / Mode
parameter).
— 1200, 2400, 4800, 9600, 19200, 38400, or 115200
baud transmission rate.
— Parity-checking (odd, even or none).
WARNING – Bodily injury
Refer to the Navigator AWT540 Commissioning
instruction (CI/AWT540-EN) before making electrical
connections.
