ONICON System-30 MODBUS BTU - Manual (Page 28)

11451 Belcher Road South, Largo, FL 33773 • USA • Tel +1 (727) 447-6140 • Fax (727) 442-5699 • [email protected]
System-30 BTU Measurement System MODBUS RTU RS485 04/14 - 0583-1 / 18345
Page 28
4.7 MODBUS MEMORY MAP
ONICON Btu meters equipped with MODBUS RTU serial communications provide volume and
energy rate data, temperature data, totalized volume and totalized energy data in a variety of
engineering units. For example, supply and return temperatures are available in both degrees F
and degrees C. You select the engineering units you wish to use by mapping to the appropriate
registers.
4.7.1 MODBUS RTU Register Format and Networking Information
1. All registers are 16 bit MODBUS Holding Registers
2. MODBUS Holding Registers are used in 4 different ways.
A. As an analog value: In some cases these values are scaled
by multiplying the register contents by a fixed multiplier.
B. As a status indicator where the register value can only
be “1” or “2”.
C. As a mode indicator where the value indicates current operating mode
such as; “1” = single, “2” = dual, or “3” = bi-directional.
D. As a control register where the host can write a value to reset total(s).
3. Registers 40001 through 40068 are unsigned integer registers (0 to 65,535) except
for 40024 and 40025. These are 16 bit signed integer values (-32,768 to +32,767).
Registers 41003 through 41064 are 32 bit single precision floating point values.
41001, 41002 and 41065 through 41069 are unsigned integer registers.
4. MODBUS function codes supported:
CODE DESCRIPTION
03 Read Holding Registers
06 Preset Single Registers
16 Preset Multiple Registers
17 Report Slave ID
5. Connection information: RS485, 2-wire (half duplex)
6. Data: 8 bits, 1 stop bit
7. Flow control (handshaking): None
8. Parity: None
9. Device address range: 1 – 247 (default address 017)
10. Termination: selectable, 120 ohms or none (default - none)