Appendix C - Modbus Communications - Qualitrol 111-300 Series Instruction Manual

A A A A C C C C – – – –
ModBus Communications
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If the Model 111L/111W is equipped with the optional RS-485 port, the unit can
communicate with a ModBus master station.
The RS-485 port terminals are located on the rear of the unit.
Terminals 28 & 30 and terminal 31 & 29 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 and 06 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 5 seconds). The unit will then be displaying the current baud
rate:
Pressing the TEST button will step the display up thru the above choices.
Pushing the MAX MEMORY button will step the display down thru the
above choices
2. When the desired baud rate is displayed, press the MANUAL FAN button,
this will show the current parity setting.
3. When the desired parity is displayed, press the MANUAL FAN 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.
If No Parity has been selected then the number of stop bits can be set to 1 or 2
(S1 or S2). S1 is used if the unit is communicating through a modem,
otherwise S2 is the standard.
4. When the desired Stop Bit is displayed, press the MANUAL FAN button, this
will show the Protocol setting:
Terminal (TB1)
28
29
30
31
15
12 = 1200 bits per second
24 = 2400
48 = 4800
96 = 9600
192 = 19200
PE for even parity (standard)
PO for Odd Parity
P-- for No parity
2 0
E l e c t r o n i c T e m p e r a t u r e M o n i t o r
Function
+Transmit
-Transmit
+Receive
-Receive
Shield Ground