/// <summary>
/// Reads multiple vars in a single request.
/// You have to create and pass a list of DataItems and you obtain in response the same list with the values.
/// Values are stored in the property "Value" of the dataItem and are already converted.
/// If you don't want the conversion, just create a dataItem of bytes.
/// The number of DataItems as well as the total size of the requested data can not exceed a certain limit (protocol restriction).
/// </summary>
/// <param name="dataItems">List of dataitems that contains the list of variables that must be read.</param>
/// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
/// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
public async Task <List <DataItem> > ReadMultipleVarsAsync(List <DataItem> dataItems, CancellationToken cancellationToken = default)
{
//Snap7 seems to choke on PDU sizes above 256 even if snap7
//replies with bigger PDU size in connection setup.
AssertPduSizeForRead(dataItems);
try
{
var dataToSend = BuildReadRequestPackage(dataItems.Select(d => DataItem.GetDataItemAddress(d)).ToList());
var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
ParseDataIntoDataItems(s7data, dataItems);
}
catch (SocketException socketException)
{
throw new PlcException(ErrorCode.ReadData, socketException);
}
catch (OperationCanceledException)
{
throw;
}
catch (Exception exc)
{
throw new PlcException(ErrorCode.ReadData, exc);
}
return(dataItems);
}