Spirax Sarco RIM20, Installation And Maintenance Instructions Manual, Page: 83 / 132

IM-P198-05 MI Issue 2 83
5.5.6 Menu Items
The following menu items are in the Output Menu and allow selection and control of the
Modbus communication protocol.
5.5.7 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.
5.5.8 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.
5.5.10 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, psi a, lbm/sec , ft 3/sec,
Btu/sec , lbm/ft 3 Display - variables are displayed in user selected display unit.
5.5.11 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.
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
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.