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// Copyright 2014 Quoc-Viet Nguyen. All rights reserved.
// This software may be modified and distributed under the terms
// of the BSD license. See the LICENSE file for details.
/*
Package modbus provides a client for MODBUS TCP and RTU/ASCII.
*/
package modbus
import (
"fmt"
)
const (
// Bit access
FuncCodeReadDiscreteInputs = 2
FuncCodeReadCoils = 1
FuncCodeWriteSingleCoil = 5
FuncCodeWriteMultipleCoils = 15
// 16-bit access
FuncCodeReadInputRegisters = 4
FuncCodeReadHoldingRegisters = 3
FuncCodeWriteSingleRegister = 6
FuncCodeWriteMultipleRegisters = 16
FuncCodeReadWriteMultipleRegisters = 23
FuncCodeMaskWriteRegister = 22
FuncCodeReadFIFOQueue = 24
)
const (
ExceptionCodeIllegalFunction = 1
ExceptionCodeIllegalDataAddress = 2
ExceptionCodeIllegalDataValue = 3
ExceptionCodeServerDeviceFailure = 4
ExceptionCodeAcknowledge = 5
ExceptionCodeServerDeviceBusy = 6
ExceptionCodeMemoryParityError = 8
ExceptionCodeGatewayPathUnavailable = 10
ExceptionCodeGatewayTargetDeviceFailedToRespond = 11
)
// ModbusError implements error interface.
type ModbusError struct {
FunctionCode byte
ExceptionCode byte
}
// Error converts known modbus exception code to error message.
func (e *ModbusError) Error() string {
var name string
switch e.ExceptionCode {
case ExceptionCodeIllegalFunction:
name = "illegal function"
case ExceptionCodeIllegalDataAddress:
name = "illegal data address"
case ExceptionCodeIllegalDataValue:
name = "illegal data value"
case ExceptionCodeServerDeviceFailure:
name = "server device failure"
case ExceptionCodeAcknowledge:
name = "acknowledge"
case ExceptionCodeServerDeviceBusy:
name = "server device busy"
case ExceptionCodeMemoryParityError:
name = "memory parity error"
case ExceptionCodeGatewayPathUnavailable:
name = "gateway path unavailable"
case ExceptionCodeGatewayTargetDeviceFailedToRespond:
name = "gateway target device failed to respond"
default:
name = "unknown"
}
return fmt.Sprintf("modbus: exception '%v' (%s), function '%v'", e.ExceptionCode, name, e.FunctionCode)
}
// ProtocolDataUnit (PDU) is independent of underlying communication layers.
type ProtocolDataUnit struct {
FunctionCode byte
Data []byte
}
// Packager specifies the communication layer.
type Packager interface {
Encode(pdu *ProtocolDataUnit) (adu []byte, err error)
Decode(adu []byte) (pdu *ProtocolDataUnit, err error)
Verify(aduRequest []byte, aduResponse []byte) (err error)
}
// Transporter specifies the transport layer.
type Transporter interface {
Send(aduRequest []byte) (aduResponse []byte, err error)
}
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