11
the least significant decimal digit). To get an actual fractional number with specified precision, scale the
register value with the given multiplier. To write a fractional number into the register, divide the number
by the given multiplier.
4.2.2 32-bit Modulo 10000 Format
The short energy registers 287-294, and 301-302 are transmitted in two contiguous 16-bit registers in
modulo 10000 format. The first (low order) register contains the value mod 10000, and the second
(high order) register contains the value/10000. To get the true energy reading, the high order register
value should be multiplied by 10,000 and added to the low order register.
4.2.3 32-bit Long Integer Format
In a 32-bit long integer format, data is transmitted in two adjacent 16-bit Modbus registers as unsigned
or signed long integer (whole) numbers. The first register contains the low-order word (lower 16 bits)
and the second register contains the high order word (higher 16 bits) of the 32-bit long number. The
low-order word always starts at an even Modbus address. The value range for unsigned data is 0 to
4,294,967,295; for signed data the range is -2,147,483,648 to 2,147,483,647.
A 32-bit data can be transmitted without conversion as is, or by using decimal pre-scaling to transform
fractional numbers to an integer format as described above (see Decimal Scaling in Section 4.2.1).
4.3 User Assignable Registers
The PM171 contains the 120 user assignable registers in the address range of 0 to 119 (see Table
4-1), any of which you can map to either register address accessible in the instrument. Registers that
reside in different locations may be accessed by a single request by re-mapping them to adjacent
addresses in the user assignable registers area.
The actual addresses of the assignable registers which are accessed via addresses 0 to 119 are
specified in the user assignable register map (see Table 4-2). This map occupies addresses from 120
to 239, where map register 120 should contain the actual address of the register accessed via
assignable register 0, register 121 should contain the actual address of the register accessed via
assignable register 1, and so on. Note that the assignable register addresses and the map register
addresses may not be re-mapped.
To build your own register map, write to map registers (120 to 239) the actual addresses you want to read from
or write to via the assignable area (0 to 119). Note that long word registers should always be aligned at even
addresses
.
For example, if you want to read registers 7136 (real-time voltage of phase A, word) and 7576/7577
(kWh import, long word) via registers 0-2, then do the following:
- write 7576 to register 120
- write 7577 to register 121
- write 7136 to register 122
Reading from registers 0-2 will return the kWh reading in registers 0 (low word) and 1 (high word), and the
voltage reading in register 2.
Table 4-1 User Assignable Registers
Register contents
Register Size, byte
Direction
Range
User definable data 0
0
User definable data 1
1
User definable data 2
...
2
...
...
...
...
User definable data 119
119
- depends on the mapped register
