Package org.openhab.core.io.transport.modbus

Class ModbusConstants

java.lang.Object

org.openhab.core.io.transport.modbus.ModbusConstants

@NonNullByDefault
public class ModbusConstants
extends Object

Constants for Modbus transport == Regarding maximum read and write limits == Maximum number of registers that are allowed to be read. The Modbus protocol has many intepretation on maximum data size of messages. Good reference is here. We try to follow modern specification here (V1.1B3). See section 4.1 Protocol Specification in the specification. According to V1.1B3, maximum size for PDU is 253 bytes, making maximum ADU size 256 (RTU) or 260 (TCP). In the spec section 6, one can see maximum values for read and write counts. Note that this is not the only interpretation -- some sources limit the ADU to 256 also with TCP. In some cases, slaves cannot take in so much data. Reads are limited by response PDU size. Writes (FC15 and FC16) are limited by write request ADU size.

Author:

Sami Salonen - Initial contribution

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static enum	ModbusConstants.ValueType	Value types for different number types.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	MAX_BITS_READ_COUNT	Maximum number of coils or discrete inputs that are allowed to be read.
static final int	MAX_BITS_WRITE_COUNT	Maximum number of coils or discrete inputs that are allowed to be written.
static final int	MAX_REGISTERS_READ_COUNT	Maximum number of registers that are allowed to be read.
static final int	MAX_REGISTERS_WRITE_COUNT	Maximum number of registers that are allowed to be written.

Constructor Summary

Constructors

Constructor	Description
ModbusConstants()

Method Summary

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

MAX_BITS_READ_COUNT

public static final int MAX_BITS_READ_COUNT

Maximum number of coils or discrete inputs that are allowed to be read. Limitation by Modbus protocol V1.1B3, 6.1 definition of Read Holding registers.

See Also:

• Constant Field Values

MAX_REGISTERS_READ_COUNT

public static final int MAX_REGISTERS_READ_COUNT

Maximum number of registers that are allowed to be read. Limitation by Modbus protocol V1.1B3, 6.3 definition of Read Coils.

See Also:

• Constant Field Values

MAX_BITS_WRITE_COUNT

public static final int MAX_BITS_WRITE_COUNT

Maximum number of coils or discrete inputs that are allowed to be written. Limitation by Modbus protocol V1.1B3, 6.11 definition of Write Multiple coils.

See Also:

• Constant Field Values

MAX_REGISTERS_WRITE_COUNT

public static final int MAX_REGISTERS_WRITE_COUNT

Maximum number of registers that are allowed to be written. Limitation by Modbus protocol V1.1B3, 6.12 definition of Write Multiple registers.

See Also:

• Constant Field Values

Constructor Details

ModbusConstants

public ModbusConstants()