12 Communication
Reading Process Data
Alicat CODA KM-Series mass flow meters make no distinction between
“Input” and “Holding” registers. Modbus function codes FC03 and FC04
can be used interchangeably to read data from the device.
Sensor and process values are stored as big-endian, 32-bit IEEE-754
floating point numbers spanning two registers. Your control system will
need to concatenate these into a single value to interpret them correctly.
Alternate registers intended to simplify re-use of code written for non-CODA
Alicat devices are included in parentheses. You can use either or both.
Writing Control and Configuration Information
All command and control requests to a CODA instrument are issued with
Modbus function code FC16: “write multiple registers”. For PID tuning
assistance, please contact Alicat.
Modbus Reading and Status Registers
Note:
All parameters in this table are read-access only.
Data Units
Data
Format
Register
Parameter
Boolean
Binary Array
1201..1202
Status Flags (next table)
kg/m³
Float
1203..1204 (2041..2042)
Density
°C
Float
1205..1206 (2043..2044)
Temperature
m³/hr
Float
1207..1208 (2045..2046)
Volumetric Flow
g/hr
Float
1209..1210 (2047..2048)
Mass Flow
g
Float
1211..1212 (2051..2052)
Total Flow
N/A (1–247 Accepted)
Unsigned Int
2053
Modbus ID
N/A (0=Gas; 1=Liquid)
Unsigned Int
2054
Process Fluid State
Boolean
Unsigned Int
2055
Volume Over-range
Boolean
Unsigned Int
2056
Mass Flow Over-range
Boolean
Unsigned Int
2057
Temperature Over-range
Boolean
Unsigned Int
2058
Totalizer Rollover
