5
GF U3000 V2 Ultrasonic Flowmeter
Modbus Supplement to the operating instructions
Baud rate and other options may be set in the Modbus Setup menu (Setup Instrument | Modbus..)
Default frame settings are as per the Modbus specification of 19200 baud, even parity and one stop bit.
In the Modbus Setup menu, the user may set the Modbus address, the baud rate, frame format and other parameters. Note that only
RTU mode is possible at the time of writing, and as such, an 8-bit byte is the only sensible selection. If 7 bits are selected in RTU
mode, then a beep will sound, and the baud rate will change to the default. Warnings will be generated if the frame format is non-
standard, but the settings may still be used. Modbus addresses may be between 1 and 247.
While some GF U3000 V2 Ultrasonic Flowmeter parameters are configurable via a management system, GF U3000 V2 Ultrasonic
Flowmeter local mode takes precedence. To stop a management system changing configuration while operating in local mode, set
Block All Remote Changes, or Block Remote Total Changes as appropriate, in the Modbus Setup menu. Blocking all remote changes
includes blocking of total changes.
When complete select Save, Configure and Exit.
3.1
Supported Messages
The following message types are supported from the Modbus Application Protocol Specification:
Message Type
Message
Number
Notes
READ HOLDING REGISTERS
03 (0x03)
Read a contiguous block of registers.
WRITE SINGLE REGISTER
06 (0x06)
Write to a single register.
WRITE MULTIPLE REGISTERS
16 (0x10)
Write to multiple registers in one transaction.
MASK WRITE REGISTER
22 (0x16)
Bits within writable registers may be set or reset with this command.
E.g., to set bit 2, set the AND mask to 0xFFFB (bit 2 low) and the OR mask to 0x0004
(bit 2 high). To clear bit 2 set the AND mask to 0xFFFB and the OR mask to 0x0000.
In general, set all bits in the AND mask to 1 except for the bit positions you wish to
modify. Set the matching bit positions in the OR mask to the value you want the bit
position to hold.
READ WRITE MULTIPLE REGISTERS 23 (0x17)
This command allows the write and subsequent read of two, possibly disjoint sets
of registers. The write operation is performed before the read operation as per the
Modbus Application Protocol Specification.
DIAGNOSTICS
08 (0x08)
Only the following sub functions:
00 Return Query Data
01 Restart Communications
04 Force Listen Only Mode
READ DEVICE IDENTIFICATION
43/14
(0x2B/0x0E)
Support to Conformance level 0x82 (Basic and Regular Identification – Stream and
individual Access).
G2.3 Modbus Messages Supported
None of these messages are supported in broadcast mode (i.e., writes to address zero).
