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F-1500 Turbine Flow Meter Manual 02/18 - 1018-6 / 35726
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the number of stop bits is 1 (non-standard) or 2. When changing the protocol, the change is
made as soon as the Enter key is pressed.
Modbus Units
The Modbus Units menu is to control which units, where applicable, the meter’s variables
will be displayed in. Internal – (these are the base units of the meter, °F, psia, lbm/sec ,
ft3/sec, Btu/sec , lbm/ft3 Display) – variables are displayed in user selected display unit.
Modbus Order
The byte order within registers and the order in which multiple registers containing floating
point or long integer data are transmitted may be changed with this menu item. According to
the Modbus specification, the most significant byte of a register is transmitted first, followed
by the least significant byte. The Modbus specification does not prescribe the order in which
registers are transmitted when multiple registers represent values longer than 16 bits. Using
this menu item, the word order and byte order for floating point and long integer values may
be reversed to accommodate different Modbus operating systems.
The following four selections are available in this menu. When selecting an item, the
protocol is changed immediately without having to press the ENTER key.
0-1:2-3
Most significant register first, most significant byte first (default)
2-3:0-1
Least significant register first, least significant byte first
1-0:3-2
Most significant register first, least significant byte first
3-2:1-0
Least significant register first, most significant byte first
Table 2. Byte Order
Note that all of the registers are affected by the byte order, including strings and registers
representing 16-bit integers. The register order only affects the order of those registers
representing 32-bit floating point and long integer data, but does not affect single 16-bit
integers or strings.
Modbus Protocol
The Modbus RTU protocol is supported in this implementation. Supported baud rates are
1200, 2400, 4800, 9600, 19200, 38400, 57600, and 115200. The default baud rate is 19200
baud. Depending upon the Modbus protocol selected, data is transmitted in 8-bit data frames
with even or odd parity and 1 stop bit or no parity and 2 or 1 (non-standard) stop bits.
The current Modbus protocol specification does not define register usage, but there is an
informal register numbering convention derived from the original (now obsolete) Modicon
Modbus protocol specification which is still used by many vendors of Modbus capable
products.
Registers
Usage
Valid Function Codes
00001–09999
Read/write bits ("coils")
01 (read coils) 05 (write single coil)
15 (write multiple coils)
10001–19999
Read-only bits ("discrete inputs")
02 (read discrete inputs)
30001–39999
Read-only 16 bit registers ("input registers"),
IEEE 754 floating point register pairs, arbi-
trary length strings encoded as two ASCII
characters per 16-bit register
03 (read holding registers) 04 (read
input registers)
40001–49999
Read/write 16-bit registers ("holding regis-
ters"), IEEE 754 floating point register pairs,
arbitrary length strings encoded as two
ASCII characters per 16-bit register
03 (read holding registers) 06 (write
single register) 16 (write multiple
registers)