Sierra INNOVA-MASS 241-VTP - Manual (Page 80)

Appendix E MODBUS Commands Series 24-HP Instruction Manual
E-2 IM-24-HP
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 contain-
ing 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.
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
Note that all of the registers are affected by the byte order, includ-
ing 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 de-
fault baud rate is 19200 baud. Depending upon the Modbus protocol selected,
data are 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