11
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.
EXAMPLES
1. Unsigned 32-bit Values
If you read unsigned Voltage V1 of 69,000V from registers 13952-13953, then the register readings will be as
follows:
(13952) = 3464
(13953) = 1
The 32-bit value is (1 x 65536 + 3464) = 69000V.
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.
4.3 User Assignable Registers
The PM172 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
Address
Register contents
Type
0
Assigned register #0
INT16
1
Assigned register #1
INT16
2
Assigned register #2
INT16
… …
…
119
Assigned register #119
INT16
Table 4-2 User Assignable Register Map
Address
Register contents
Type
R/W
Range
120
Mapped address for register #0
UINT16 R/W
256 to 65535
121
Mapped address for register #1
UINT16 R/W
256 to 65535
122
Mapped address for register #2
UINT16 R/W
256 to 65535
… …
…
… …
239
Mapped address for register #119
UINT16 R/W
256 to 65535
