AERCO Modbus Communications Manual - Manual (Page 54)

GF-114
MODBUS
Communication
Chapter 3
OMM-0035_0C USER MANUAL Standard Application Operations
Page 54 of 200 AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913 • Ph.: 800-526-0288 05/18/12
Simultaneous RS232 & RS485 Access to C-More Controller Variables
As previously mentioned, read and write access of the C-More Controller variables are
protected from unauthorized access by an internal security level hierarchy. Passwords may be
entered in the Slave’s Holding Registers using any of the following methods:
• Locally via the front panel keypad and display
• Remotely via the front panel RS232 port
• Remotely via the Modbus (RS485) interface
It is imperative that the user understands that the LAST change made to any menu variable
(including passwords) will supersede any previous change, regardless of which of the above
methods is used. There is no priority structure assigned to any of the above methods and since
they are not interlocked, they may be performed concurrently.
3.2.2 Direct Drive Control
In the Direct Drive Mode, the holding register parameter “Net Direct Drive” (address 0x0001)
must be written or broadcast periodically from the BMS/BMS II/ACS (or EMS Master) to all
Slave Controllers on the network. The Modbus message will specify the Fire Rate (0 to 100%)
for the addressed Slave(s). If the Net Direct Drive message is broadcast, all enabled network
Slaves will be set to the same fire rate percentage. However, if different fire rates are required
for specific Slaves, each Slave must be addressed individually. Each time a network Slave
successfully receives the Net Direct Drive message, it will reset its Heartbeat Timer which has a
fixed 10 second timeout. If this timeout period is exceeded, the C-More Controller Slave will
default to “Fail-Safe Mode” (Shutdown or Constant Setpoint) stored in holding register address
0x0018. When this occurs, “Modbus Comm Fault” will be displayed.
During operation in the Direct Drive Mode, only the Net Direct Drive variable in the Slave’s
Holding Register can be remotely adjusted. If desired, manual control via the C-More Controller
front panel can be invoked by pressing the AUTO/MAN switch on the front panel.
3.2.3 Remote Setpoint Control
In the Remote Setpoint Mode, the holding register parameter “Net Remote Setpoint” (address
0x0000) must be written or broadcast periodically from the BMS/BMS II (or EMS Master) to all
Slave Controllers on the network. The Modbus message will specify the Setpoint Temperature
for the addressed Slave(s). If the Net Remote Setpoint message is broadcast, all enabled
network Slaves will be set to the same setpoint temperature. However, if different setpoint
temperatures are required for specific Slaves, each Slave must be addressed individually. Each
time a network Slave successfully receives the Net Remote Setpoint message, it will reset its
“Heartbeat”. For C-More Controllers, the “Heartbeat” timeout is fixed at 10 seconds. If this
timeout period is exceeded, the C-More Controller Slave will default to “Fail-Safe Mode” and
display a “Modbus Comm Fault”.
During operation in the Remote Setpoint Mode, only the “Net Remote Setpt” variable in the
Slave’s Holding Register can be remotely adjusted. If desired, manual control via the C-More
Controller front panel can be invoked by pressing the AUTO/MAN switch on the front panel.