FORM NO.: 6U5M-A11M-NB-EN
JOHNSON CONTROLS 47
MODBUS PROTOCOL
TABLE 15 - DEFINITIONS
NO.
ITEM DESCRIPTION
1 Data Flow
Communication Baud rate: 9600bps;
8-N-1: 1 start bit,1 stop bit, check bit-none, 8 data bits;
Modbus-RTU Protocol;
CRC: Cyclic Redundancy Check;
Hexadecimal data.
2 Master - Slave
Modbus as master;
1# microboard as slave.
3 Temperature
Unit: 0.1℃
Actual temperature=Register value/10
e.g.: Cooling LWT=81, then the actual temperature is 8.1℃
4 Read/Write Mechanism
BAS need to keep communication with mainboard periodically;
BAS parameter setpoint may exceed unit default range and it is required for BAS to
read the setpoints from the mainboard.
5 BAS Enable
The BAS Modbus addresses of subordinates are set through HMI;
Set DIP 301-7 to “ON” to make BAS enable.
Set the corresponding parameters in HMI to enable and disable the BAS Start/Stop
and Operating Mode functions.
6 Start/Stop Status
The Start/Stop Command (Register value = 0) is only used to start/stop the unit;
Actual Start/Stop Status is accessible by reading Register value = 100.
TABLE 16 – SYSTEM SETPOINTS
NO.
Name Function Code
Register
Address
Note
System Setpoints
1 Chiller ON/OFF 3, 6, 16 0 0-Invalid, 1-On, 2-Off
2 Mode Setting 3, 6, 16 1 0-Cooling, 1-Heating, 8-Only Pump
3 Cool Return WT Setpoint 3, 6, 16 2 10~30
4 Heat Return WT Setpoint 3, 6, 16 3 25~50
5 Cool Leaving WT Setpoint 3, 6, 16 4 5~25
6 Heat Leaving WT Setpoint 3, 6, 16 5 30~55
7 Low Sound Mode 3, 6, 16 7 1-Enabled
8 Fault Reset 3, 6, 16 8 1-Reset
9 Cooling Control Select 3, 6, 16 9 0-Fixed RT, 1-Fixed LT
10 Heating Control Select 3, 6, 16 10 0-Fixed RT, 1-Fixed LT
11 Temperature Control Cycle 3, 6, 16 11 20~120, Unit: s
12 Water Temp. Control Diff. 3, 6, 16 12 1~3
Cooke Industries - Phone: +64 9 579 2185 Email: sales@cookeindustries.co.nz Web: www.cookeindustries.co.nz
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