Modbus Function Codes, Exception Codes

Variables
static const uint8_t	ModbusMaster::ku8MBIllegalFunction = 0x01
	Modbus protocol illegal function exception. More...
static const uint8_t	ModbusMaster::ku8MBIllegalDataAddress = 0x02
	Modbus protocol illegal data address exception. More...
static const uint8_t	ModbusMaster::ku8MBIllegalDataValue = 0x03
	Modbus protocol illegal data value exception. More...
static const uint8_t	ModbusMaster::ku8MBSlaveDeviceFailure = 0x04
	Modbus protocol slave device failure exception. More...
static const uint8_t	ModbusMaster::ku8MBSuccess = 0x00
	ModbusMaster success. More...
static const uint8_t	ModbusMaster::ku8MBInvalidSlaveID = 0xE0
	ModbusMaster invalid response slave ID exception. More...
static const uint8_t	ModbusMaster::ku8MBInvalidFunction = 0xE1
	ModbusMaster invalid response function exception. More...
static const uint8_t	ModbusMaster::ku8MBResponseTimedOut = 0xE2
	ModbusMaster response timed out exception. More...
static const uint8_t	ModbusMaster::ku8MBInvalidCRC = 0xE3
	ModbusMaster invalid response CRC exception. More...

Detailed Description

Variable Documentation

ku8MBIllegalFunction

const uint8_t ModbusMaster::ku8MBIllegalFunction = 0x01

static

Modbus protocol illegal function exception.

The function code received in the query is not an allowable action for the server (or slave). This may be because the function code is only applicable to newer devices, and was not implemented in the unit selected. It could also indicate that the server (or slave) is in the wrong state to process a request of this type, for example because it is unconfigured and is being asked to return register values.

ku8MBIllegalDataAddress

const uint8_t ModbusMaster::ku8MBIllegalDataAddress = 0x02

static

Modbus protocol illegal data address exception.

The data address received in the query is not an allowable address for the server (or slave). More specifically, the combination of reference number and transfer length is invalid. For a controller with 100 registers, the ADU addresses the first register as 0, and the last one as 99. If a request is submitted with a starting register address of 96 and a quantity of registers of 4, then this request will successfully operate (address-wise at least) on registers 96, 97, 98, 99. If a request is submitted with a starting register address of 96 and a quantity of registers of 5, then this request will fail with Exception Code 0x02 "Illegal Data Address" since it attempts to operate on registers 96, 97, 98, 99 and 100, and there is no register with address

Examples:

examples/PhoenixContact_nanoLC/PhoenixContact_nanoLC.pde.

ku8MBIllegalDataValue

const uint8_t ModbusMaster::ku8MBIllegalDataValue = 0x03

static

Modbus protocol illegal data value exception.

A value contained in the query data field is not an allowable value for server (or slave). This indicates a fault in the structure of the remainder of a complex request, such as that the implied length is incorrect. It specifically does NOT mean that a data item submitted for storage in a register has a value outside the expectation of the application program, since the MODBUS protocol is unaware of the significance of any particular value of any particular register.

ku8MBSlaveDeviceFailure

const uint8_t ModbusMaster::ku8MBSlaveDeviceFailure = 0x04

static

Modbus protocol slave device failure exception.

An unrecoverable error occurred while the server (or slave) was attempting to perform the requested action.

ku8MBSuccess

const uint8_t ModbusMaster::ku8MBSuccess = 0x00

static

ModbusMaster success.

Modbus transaction was successful; the following checks were valid:

• slave ID
• function code
• response code
• data
• CRC

Examples:

examples/Basic/Basic.pde, and examples/RS485_HalfDuplex/RS485_HalfDuplex.ino.

ku8MBInvalidSlaveID

const uint8_t ModbusMaster::ku8MBInvalidSlaveID = 0xE0

static

ModbusMaster invalid response slave ID exception.

The slave ID in the response does not match that of the request.

ku8MBInvalidFunction

const uint8_t ModbusMaster::ku8MBInvalidFunction = 0xE1

static

ModbusMaster invalid response function exception.

The function code in the response does not match that of the request.

ku8MBResponseTimedOut

const uint8_t ModbusMaster::ku8MBResponseTimedOut = 0xE2

static

ModbusMaster response timed out exception.

The entire response was not received within the timeout period, ModbusMaster::ku8MBResponseTimeout.

ku8MBInvalidCRC

const uint8_t ModbusMaster::ku8MBInvalidCRC = 0xE3

static

ModbusMaster invalid response CRC exception.

The CRC in the response does not match the one calculated.