Electronic Temperature Monitor
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A
PPENDIX
E
–
ModBus Communications
If the Model 118 is equipped with the optional RS-485 port, the unit can
communicate with a ModBus master station.
The RS-485 port is located on the side of the Model 118 and is provided with a
plug-in terminal block connector. The connector is wired as follows:
When the RS-485 connector is plugged in with terminals 6 & 7 connected, the RS-
232 data function is disabled.
Terminals 1 & 3 and terminal 2 & 4 can be connected together if a 2-wire RS-485
data link is desired.
The data communicated on the RS-485 link is in ModBus RTU format. The table
included shows the data and ModBus register addresses used. Modbus functions
03, 06 and 16 are supported.
The ModBus Data Link parameters can either be set using the User Setup
software or they can be set up by the following procedure using front panel
switches:
1. Hold all three switches depressed until the unit stops cycling thru the readings
(approximately 10 seconds). The unit will then be displaying the current baud
rate:
12 = 1200 bits per second
24 = 2400
48 = 4800
96 = 9600
192 = 19200
Pressing the AUDIBLE (middle) button will step the display up thru the above
choices. Pushing the MAX MEMORY (bottom) button will step the display
down thru the above choices
2. When the desired baud rate is displayed, press the MANUAL FAN (top)
button, this will show the current parity setting.
PE for even parity (standard)
PO for Odd Parity
P-- for No parity
3. When the desired parity is displayed, press the MANUAL FAN (top) button,
this will show the current stop bit setting. If parity is even or odd the display
will show S1 and will not be able to be changed.
Terminal – TB4
Function
1
+Receive
2
-Receive
3
+Transmit
4
-Transmit
5
Shield Ground
6 & 7
Jumper together to
indicate RS485 is active