80
Designs, materials, weights and performance ratings are approximate and subject to change without notice. Visit
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international.com for up-to-date information.
Serial Communications – continued
Menu Items
The following menu items are in the Output Menu and allow selection and control of the Modbus communication
protocol.
Address
When the Modbus protocol is selected, the Modbus address is equal to the user programmable device address if it
is in the range 1…247, in accordance with the Modbus specification. If the device address is zero or is greater than
247, then the Modbus address is internally set to 1.
Comm Protocol
The Comm Protocol menu allows selection of “Modbus RTU Even,” “Modbus RTU Odd,” or “Modbus RTU None2,” or
“Modbus RTU None1,” (non-standard Modbus) with Even, Odd and None referring to the parity selection. When even
or odd parity is selected, the unit is configured for 8 data bits, 1 parity bit and 1 stop bit; with no parity, 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 what units, where applicable, the meter’s variables will be displayed in. Internal
– these are the base units of the meter, °F, psia, lbm/sec , ft
3
/sec, Btu/sec , lbm/ft
3
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 order in which registers representing floating point or long integer data and/or the byte
order within the registers may be reversed for compatibility with some PLCs and PC software.
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.
Table 4-1.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.
0-1:2-3
Most significant register first, most significant byte first (default)
2-3:0-1
Least significant register first, most significant byte first
1-0:3-2
Most significant register first, least significant byte first
3-2:1-0
Least significant register first, least significant byte first
