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writemultiplecoilsrequest.go
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writemultiplecoilsrequest.go
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package packet
import (
"encoding/binary"
"fmt"
"math/rand"
)
// WriteMultipleCoilsRequestTCP is TCP Request for Write Multiple Coils (FC=15)
//
// Example packet: 0x01 0x38 0x00 0x00 0x00 0x08 0x11 0x0F 0x04 0x10 0x00 0x03 0x01 0x05
// 0x01 0x38 - transaction id (0,1)
// 0x00 0x00 - protocol id (2,3)
// 0x00 0x08 - number of bytes in the message (PDU = ProtocolDataUnit) to follow (4,5)
// 0x11 - unit id (6)
// 0x0F - function code (7)
// 0x04 0x10 - start address (8,9)
// 0x00 0x03 - count of coils to write (10,11)
// 0x01 - coils byte count (12)
// 0x05 - coils data (13, ...)
type WriteMultipleCoilsRequestTCP struct {
MBAPHeader
WriteMultipleCoilsRequest
}
// WriteMultipleCoilsRequestRTU is RTU Request for Write Multiple Coils (FC=15)
//
// Example packet: 0x11 0x0F 0x04 0x10 0x00 0x03 0x01 0x05 0xFF 0xFF
// 0x11 - unit id (0)
// 0x0F - function code (1)
// 0x04 0x10 - start address (2,3)
// 0x00 0x03 - count of coils to write (4,5)
// 0x01 - coils byte count (6)
// 0x05 - coils data (7, ...)
// 0xFF 0xFF - CRC16 (n-2,n-1) // FIXME: add correct crc value example
type WriteMultipleCoilsRequestRTU struct {
WriteMultipleCoilsRequest
}
// WriteMultipleCoilsRequest is Request for Write Multiple Coils (FC=15)
type WriteMultipleCoilsRequest struct {
UnitID uint8
StartAddress uint16
CoilCount uint16
Data []byte
}
// NewWriteMultipleCoilsRequestTCP creates new instance of Write Multiple Coils TCP request
func NewWriteMultipleCoilsRequestTCP(unitID uint8, startAddress uint16, coils []bool) (*WriteMultipleCoilsRequestTCP, error) {
coilsCount := len(coils)
if coilsCount == 0 || coilsCount > 1968 {
// 1968 coils is due that coils byte len size field is 1 byte so max 246*8=1968 coils can be sent
return nil, fmt.Errorf("coils count is out of range (1-1968): %v", coilsCount)
}
coilsBytes := CoilsToBytes(coils)
return &WriteMultipleCoilsRequestTCP{
MBAPHeader: MBAPHeader{
TransactionID: uint16(1 + rand.Intn(65534)),
ProtocolID: 0,
},
WriteMultipleCoilsRequest: WriteMultipleCoilsRequest{
UnitID: unitID,
// function code is added by Bytes()
StartAddress: startAddress,
CoilCount: uint16(coilsCount),
Data: coilsBytes,
},
}, nil
}
// Bytes returns WriteMultipleCoilsRequestTCP packet as bytes form
func (r WriteMultipleCoilsRequestTCP) Bytes() []byte {
length := r.len()
result := make([]byte, tcpMBAPHeaderLen+length)
r.MBAPHeader.bytes(result[0:6], length)
r.WriteMultipleCoilsRequest.bytes(result[6 : 6+length])
return result
}
// ExpectedResponseLength returns length of bytes that valid response to this request would be
func (r WriteMultipleCoilsRequestTCP) ExpectedResponseLength() int {
// response = 6 header len + 1 UnitID + 1 functionCode + 2 start addr + 2 count of coils
return 6 + 6
}
// NewWriteMultipleCoilsRequestRTU creates new instance of Write Multiple Coils RTU request
func NewWriteMultipleCoilsRequestRTU(unitID uint8, startAddress uint16, coils []bool) (*WriteMultipleCoilsRequestRTU, error) {
coilsCount := len(coils)
if coilsCount == 0 || coilsCount > 1968 {
// 1968 coils is due that coils byte len size field is 1 byte so max 246*8=1968 coils can be sent
return nil, fmt.Errorf("coils count is out of range (1-1968): %v", coilsCount)
}
coilsBytes := CoilsToBytes(coils)
return &WriteMultipleCoilsRequestRTU{
WriteMultipleCoilsRequest: WriteMultipleCoilsRequest{
UnitID: unitID,
// function code is added by Bytes()
StartAddress: startAddress,
CoilCount: uint16(coilsCount),
Data: coilsBytes,
},
}, nil
}
// Bytes returns WriteMultipleCoilsRequestRTU packet as bytes form
func (r WriteMultipleCoilsRequestRTU) Bytes() []byte {
pduLen := r.len() + 2
result := make([]byte, pduLen)
bytes := r.WriteMultipleCoilsRequest.bytes(result)
crc := CRC16(bytes[:pduLen-2])
result[pduLen-2] = uint8(crc)
result[pduLen-1] = uint8(crc >> 8)
return result
}
// ExpectedResponseLength returns length of bytes that valid response to this request would be
func (r WriteMultipleCoilsRequestRTU) ExpectedResponseLength() int {
// response = 1 UnitID + 1 functionCode + 2 start addr + 2 count of coils + 2 CRC
return 6 + 2
}
// FunctionCode returns function code of this request
func (r WriteMultipleCoilsRequest) FunctionCode() uint8 {
return FunctionWriteMultipleCoils
}
func (r WriteMultipleCoilsRequest) len() uint16 {
return 7 + uint16(len(r.Data))
}
// Bytes returns WriteMultipleCoilsRequest packet as bytes form
func (r WriteMultipleCoilsRequest) Bytes() []byte {
return r.bytes(make([]byte, r.len()))
}
func (r WriteMultipleCoilsRequest) bytes(bytes []byte) []byte {
bytes[0] = r.UnitID
bytes[1] = FunctionWriteMultipleCoils
binary.BigEndian.PutUint16(bytes[2:4], r.StartAddress)
binary.BigEndian.PutUint16(bytes[4:6], r.CoilCount)
bytes[6] = uint8(len(r.Data))
copy(bytes[7:], r.Data)
return bytes
}
// CoilsToBytes converts slice of coil states (as bool values) to byte slice.
func CoilsToBytes(coils []bool) []byte {
cLen := len(coils)
cnt := cLen / 8
if cLen%8 != 0 {
cnt++
}
result := make([]byte, cnt)
for i := 0; i < cLen; i++ {
bit := i % 8
nthByte := i / 8
if coils[i] == true {
v := result[nthByte] | (1 << bit)
result[nthByte] = v
}
}
return result
}