Applied-motion SV7-Q-EE Manuel d'utilisateur télécharger pdf (Page 17)

6/26/2010

920‐0032a3eSCLCommunicationReferenceManual Page17

Pollingiseasiertocodebutlessefficientbecauseyo umusteithersitinaloopwaitingforanexpected

responseorrunatimertoperiodicallycheckfordatacomingin.Sincethechoicedependsonyour

programmingstyleandtherequirementsofyourapplication,wepresentbothtechniques.

Pollingforanincomingpacket

ThesameUdpClientobjectthatyouusetosendpacketscanbeusedtoretrieveincomingresponsesfromthe

drive.TheAvailableproperty willbegreaterthanzeroifapackethasbeenreceived.Toretrieveapacket,

assigntheReceivepropertytoaBytearray.YoumustcreateanIPEndPoint objectinordertousetheReceive

property.

private void UDPpoll()

{

// you can call this from a timer event or a loop

if (udpClient.Available > 0) // is there a packet ready?

{

IPEndPoint RemoteIpEndPoint = new IPEndPoint(IPAddress.Any, 0);

try

{

// Get the received packet. Receive method blocks

// until a message returns on this socket from a remote host,

// so always check .Available to see if a packet is ready.

Byte[] receiveBytes = udpClient.Receive(ref RemoteIpEndPoint);

// strip opcode

Byte[] SCLstring = new byte[receiveBytes.Length - 2];

for (int i = 0; i < SCLstring.Length; i++)

SCLstring[i] = receiveBytes[i + 2];

string returnData = Encoding.ASCII.GetString(SCLstring);

AddToHistory(returnData);

}

catch (Exception ex)

{

// put your error handler here

Console.WriteLine(ex.ToString());

}

Creatingareceiveeventusingacallbackfunction

First,createafunctiontohandleincomingpackets.Thisfunctionmustcontaintwolocalobjects:aUdpClient

andanIPEndPoint.ThecallbackfunctionwillbepassedanIAsyncResultobjectthatcontainsareferenceto

theUDPconnection.ThelocalIPEn dPointobjectispassedtotheUDPClient’sEndReceivepropertytoretrieve

thepacket.

public void ReceiveCallback(IAsyncResult ar)

{

int opcode;

UdpClient u = (UdpClient)((UdpState)(ar.AsyncState)).u;

IPEndPoint e = (IPEndPoint)((UdpState)(ar.AsyncState)).e;

Byte[] receiveBytes = u.EndReceive(ar, ref e);

// get opcode

opcode = 256 * receiveBytes[0] + receiveBytes[1];

if (opcode == 7) // SCL response

{

string receiveString = Encoding.ASCII.GetString(receiveBytes);

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Applied-motion SV7-Q-EE Manuel d'utilisateur Page 17

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