Chapter 1. Programming Site Data
44 DigitalFlow™ DF868 Multipurpose Ultrasonic Liquid Flowmeter Programming Manual (2-Channel)
1.7.9 MODBUS Register Map
When equipped with the optional MODBUS output card, the DF868 flow transmitter can send flow data and
diagnostic information to a flow computer (or SCADA) serially, using a Gould-type RTU protocol. In this case, only the
MODBUS function command, 3 (read multiple registers), 6 (write multiple registers) is valid. The format for the data
exchange is as follows:
• The send command (initiated by the host flow computer or controller) comes in the form:
[time delimiter]<Addr><3><First Register MSB>
<First Register LSB><Register Count MSB>
<Register Count LSB><CRC Low><CRC High>[time delimiter]
• The response (initiated by the host flow computer or controller) comes in the form:
[time delimiter]<Addr><3><Byte count><Data.........>
<CRC Low><CRC High>[time delimiter]
The format for the returned data types is as follows:
• Integer (16 bit Integer) <MSB><LSB>
1 Register - 16 bit integer
• Integer (32 bit IntegerI) <MSB><LSB><LSB><LSB>
2 Register - 32 bit integer
• Floating Point (FP) <EXP><MAN><MAN><MAN>
2 Registers - 32 bit IEEE floating point number
To request specific parameters from the DF868 via the MODBUS, the control system must access the appropriate
register number, as shown in Table 26 on the next page. Only registers 1-108 are available with the DF868 for MODBUS
communications. Registers 508-512 are used by the DF868 to store the MODBUS parameters.
Note: If you request Ch2 or AVE data from a 1-Channel meter, the values will all be zero.
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