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2. Signed 32-bit Values
If you read signed kW of -789kW from registers 14336-14337, then the register readings will be:
(14336) = 64747 (unsigned)
(14337) = 65535 (unsigned) or -1(signed value).
To take the high order register as a signed value, compare it with 32767. If the value is less
or equal to 32767, use it as is. If it is greater than 32767, then this is a negative number in
a two's complement code (like in our example) - just subtract it from 65536 to get the
original negative value.
The 32-bit reading is (-1 x 65536 + 64747) = -789kW.
Fractional 32-bit data is transmitted using a decimal pre-multiplier to pass fractional
numbers in an integer format. Fractional numbers are pre-multiplied by 10 to the power N,
where N is the number of digits in the fractional part. For example, the frequency reading of
50.01 Hz is transmitted as 5001, having been pre-multiplied by 100.
Whenever a data register contains a fractional number, the register measurement unit is
given with a multiplier
×
0.1,
×
0.01 or
×
0.001, showing the weight of the least significant
decimal digit. To get an actual fractional number with specified precision, multiply the
register value by the given multiplier. To write a fractional number into the register, divide
the number by the given multiplier.
2.6.3 32-bit Modulo-10000 Format
Energy counters 287-294 and 301-302 are read in two contiguous 16-bit registers in a
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.
2.7 User Assignable Registers
The PM174 contains 120 user assignable registers in the address range of 0 to 119, any of
which you can map to any 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
through 119, are specified in the register map (registers 120 through 239), where register
120 contains the actual address of the register accessed via register 0, register 121
contains the actual address of the register accessed via register 1, and so on. The
assignable registers and the map registers themselves 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 (registers 0 to 119). 32-bit long
registers should always be aligned at even addresses. For example, if you want to read
registers 7136 (1-second V1 voltage, scaled short integer) and 14720-14721 (kWh Import,
long integer) via registers 0-2, do the following:
- write 14720 to register 120
- write 14721 to register 121
- write 7136 to register 122
Reading from registers 0-2 will return the kWh reading in registers 0 (low 16 bits) and 1
(high 16 bits), and the voltage reading in register 2.
2.8 Password Protection
The PM174 has a password protection option allowing you to protect your setups,
cumulative registers and logs from being changed or cleared through communications. You
can disable or enable password protection through communications or via the front display.
For details, refer to your instrument Installation and Operation Manual.
