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Application and Installation Guide EMCP 4 SCADA Data Links

ABLE 4-5: WRITE MULTIPLE REGISTERS - REQUEST

Address Fcn Code Addr hi Addr lo Num hi Num lo Byte Ct

Slave addr. 0x10 Reg address Number of Registers (N) N x 2

Data 1 hi Data 1 lo … Data N hi Data N lo CRC lo CRC hi

TABLE 4-6: WRITE MULTIPLE REGISTERS - RESPONSE

Address Fcn Code Addr hi

ddr lo Num hi Num lo CRC lo CRC hi

Slave addr. 0x10 Starting Reg address Number of Registers (N) CRC16 error checking

NOTE: For EMCP 4 controller software version 4.2 PROD and beyond, all control-related write register

capabilities are DISABLED by default. Modbus control via write registers can be enabled by

configuring the “Remote Genset Control Enable Status” setpoint under CONFIGURE > ALL

SETPOINTS > CONTROL > AUTO START/STOP.

4.3 DATA INTERPRETATION

In order to send data, or once data is received, it must be interpreted. A single piece of data can span

multiple Modbus registers. There are a few different types of data:

 Numerical data

 State-based data

 Complex data

On PC systems, register data is converted to numbers according to predefined data types. The EMCP 4

data should always be converted to unsigned data types. The specific data type depends on the PC

system architecture. For example, if UINT data type is 16-bit, then it can be used for single register reads.

For data points that span 2 registers, they must use a longer data type (or calculate the value manually

from two separate UINTs), such as ULONG. But again, the data types available and their length are

system-specific. ULONG may be 32-bit or 64-bit or may not even be supported at all.

If converting the data manually, in order to interpret the data, first the bits must be converted to a raw

number, where the number represents the decimal (base-10) representation of the raw data. Modbus

data is sent most-significant-bit first and most-significant-byte first, and for data spanning multiple

registers, the lowest number register is most significant. The EMCP 4 uses unsigned integer

representations of all the data. Negative values for numerical data are calculated (see Numerical Data

section below) by doing math operations on the unsigned integer value.

Two-register data points should be treated as 4-byte unsigned integers. Example of data received from a

two-register read (spaces added for readability). Note that the response sends the lower number register

first, followed by the higher number register. Therefore, the lower number register is more significant:

Binary data received (in order of receipt): 0b 0000 0000 0000 0000 0000 0110 1000 1111

Raw data in hexadecimal: 0x 0000 068F

Raw data in decimal: 1,679

The rest of the interpretation process depends on the type of data being read.