Modbus Registers

Table of Standard Dataset Common Registers

The main information needed for remote supervision of a ComPact NSX, ComPact NS, MasterPact NT/NW or MasterPact MTZ circuit breaker is contained in the table of common registers starting at register 32000.

One Modbus read request is limited to 125 registers maximum. Three Modbus read requests are necessary to read the entire table.

It contains the following information:

Circuit breaker status
Tripping causes
Real-time values of main measurements: current, voltage, power, and energy

The content of this table of registers is detailed in Standard Dataset Common Registers.

Use of these common registers is highly recommended to optimize response times and simplify the use of data.

Table Format

Address	Register	RW	Unit	Type	Range	A/E	A/E/P/H	X	Description

Address: a 16-bit register address in hexadecimal. The address is the data used in the Modbus frame.
Register: a 16-bit register number in decimal (register = address + 1).
RW: register read-write status
- R: the register can be read by using Modbus functions
- W: the register can be written by using Modbus functions
- RW: the register can be read and written by using Modbus functions
- RC: the register can be read by using the command interface
- WC: the register can be written by using the command interface
Unit: the unit the information is expressed in.
Type: the encoding data type (see data type description below).
Range: the permitted values for this variable, usually a subset of what the format allows.
A/E: types of ComPact NSXMicroLogic trip unit for which the register is available.
- Type A (Ammeter): current measurements
- Type E (Energy): current, voltage, power, and energy measurements
A/E/P/H: types of MasterPact NT/NW and ComPact NSMicroLogic trip unit for which the register is available.
- Type A (Ammeter): current measurements
- Type E (Energy): current, voltage, power, and energy measurements
- Type P (Power): current, voltage, power, energy measurements, and advanced protection
- Type H (Harmonics): current, voltage, power, energy, energy quality measurements, and advanced protection
X: register available in the MicroLogic X control unit for MasterPact MTZ circuit breakers.
Description: provides information about the register and restrictions that apply.

Data Types

Data Types	Description	Range
INT16U	16-bit unsigned integer	0 to 65535
INT64	64-bit signed integer	- 9 223 372 036 854 775 808 to + 9 223 372 036 854 775 807
INT64U	64-bit unsigned integer	0 to 18 446 744 073 709 600 000
FLOAT32	32-bit signed integer with a floating point	2^-126 (1.0) to 2¹²⁷ (2 - 2^-23)

Big-Endian Format

INT64 and INT64U variables are stored in big-endian format: the most significant register is transmitted first and the least significant register is transmitted at last place.

INT64 and INT64U variables are made of INT16U variables.

The formulas to calculate the decimal value of these variables are:

INT64: (0-bit63)x2⁶³ + bit62x2⁶² + bit61x2⁶¹ + ...bit1x2¹ + bit0x2⁰
INT64U: bit63x2⁶³ + bit62x2⁶² + bit61x2⁶¹ + ...bit1x2¹ + bit0x2⁰

Example:

The total active energy in the standard dataset is an INT64 variable coded in registers 32096 to 32099.

If the values in the registers are:

register 32096 = 0
register 32097 = 0
register 32098 = 70 (0x0046) 0x0017 or 23
register 32099 = 2105 (0x0839) 0x9692 or 38546 as INT16U variable and -26990 as INT16 variable (use the INT16U value to calculate the value of the total active energy).

Then the total active energy is equal to 0x2⁴⁸ + 0x2³² + 23x2¹⁶ + 38546x2⁰ = 1545874 Wh.

Data Type: FLOAT32

Data type FLOAT32 is represented in the single precision IEEE 754 (IEEE standard for floating-point arithmetic). A value N is calculated as indicated below:

N = (-1)^S x 2^E-127 x (1+M)

Coefficient	Stands for	Description	Number of Bits
S	Sign	Defines the sign of the value: 0 = positive 1 = negative	1 bit
E	Exponent	Excess 127 binary integer added. When 0 < E < 255, the actual exponent is: e = E - 127.	8 bits
M	Mantissa	Magnitude, normalized binary significant	23 bits

Coefficient

Stands for

Description

Number of Bits

Sign

Defines the sign of the value:

0 = positive

1 = negative

1 bit

Exponent

Excess 127 binary integer added.

When 0 < E < 255, the actual exponent is: e = E - 127.

8 bits

Mantissa

Magnitude, normalized binary significant

23 bits

Example:

0 = 0 00000000 00000000000000000000000

-1.5 = 1 01111111 10000000000000000000000

with:

S = 1
E = 01111111 = 127
M = 10000000000000000000000 = 1x2^-1 + 0x2^-2 +...+ 0x2^-23 = 0.5
N = (-1) x 2⁰ x (1+0.5) = -1.5

Quality of Bits in Registers

The quality of each bit of a register coded as INT16U data type as an enumeration of bits can be indicated in the register preceding the register.

Example:

The quality of each bit of the register 32001, circuit breaker status, is given in the preceding register, 32000.

The quality of the data corresponding to the bit 0 of register 32001, OF status indication contact, is given in the bit 0 of register 32000:

bit 0 of register 32000 = quality of OF status indication
bit 0 of register 32001 = OF status indication contact

If	Then
If bit 0 of register 32000 = 1 AND bit 0 of register 32001 = 0	The OF contact indicates that the device is open
If bit 0 of register 32000 = 1 AND bit 0 of register 32001 = 1	The OF contact indicates that the device is closed
If bit 0 of register 32000 = 0	The OF contact indication is invalid