SerialLineControlADS

The function block SerialLineControlADS handles the communication between a virtual serial interface and the PLC. The function block is called cyclically, and places received data into the RxBuffer. Data made available in the transmit buffer TxBuffer is sent to the interface at the same time.

Since the function is handled independent of the application, it is referred to as background communication. Just like the function block SerialLineControl, it can also be handled in a fast task. Normally, however, the function block can be called in the standard task and a separate second, faster task can be dispensed with. (see communication concept and assisted hardware).

When the function block is called cyclically and the input Connect is set, the parameterized serial COM port is opened automatically.
This means that this COM port is blocked for other applications. To enable the COM port for access from another application, you can reset the input Connect. The current port is then closed. If a different COM port or a different parameterization is selected in the input structure SerialCfg, the previous port is closed automatically and the new port is opened.

Inputs

VAR_INPUT
  Connect    : BOOL;   (* connect to serial port [TRUE=connect, FALSE=disconnect] *)
  SerialCfg  : ComSerialConfig;
  NetId      : T_AmsNetId := '';            (* host NetId *)
  Timeout    : TIME := DEFAULT_ADS_TIMEOUT; (* Timeout for ADS calls *)
END_VAR

Name	Type	Description
Connect	BOOL	To initialize a connection to a serial port, Connect TRUE must be applied to the function block. If Connect is FALSE, an opened port is closed again. Note: If a change of this input variable is executed, it can take a maximum of 6 times the timespan specified at Timeout until the action has been completely executed. Therefore, the application must pay attention to the PortOpened output and wait until it assumes the desired state.
SerialCfg	ComSerialConfig	This input structure defines which COM port is to be used and opened with which parameters.
NetId	T_AmsNetId	To execute the query on the local device, it is not necessary to specify this input variable. Alternatively, an empty string can be specified. To direct the request to another TwinCAT target device, the corresponding AMS Net Id can be specified here.
Timeout	TIME	Specifies a maximum duration of time for the execution of the function block. The default value is 5 seconds. (A value of at least 1000 ms should be specified)

Inputs/outputs

VAR_IN_OUT
  TxBuffer         : ComBuffer;
  RxBuffer         : ComBuffer;
END_VAR

Name	Type	Description
TxBuffer	ComBuffer	Buffer with send data for the serial interface being used. The transmit buffer is filled by functions such as SendByte, SendData or SendString.
RxBuffer	ComBuffer	Buffer into which received data is placed. The receive buffer is read by functions such as ReceiveByte, ReceiveData or ReceiveString.

Outputs

VAR_OUTPUT
  PortOpened : BOOL;   (* Indicates if selected serial port is opened *)
  Error      : BOOL;   (* 'TRUE' if an error occurred *)
  ErrorID    : UDINT;  (* Displays the error code; 0 = no error *)
  Busy       : BOOL;   (* 'TRUE' if internal ADS communication is busy *)
  TxBufCount : UDINT;  (* number of bytes in internal Tx buffer *)
  RxBufCount : UDINT;  (* number of bytes in internal Rx buffer *)
END_VAR

Name	Type	Description
PortOpened	BOOL	This output indicates whether the selected serial port is opened and linked.
Error	BOOL	This output Error goes TRUE as soon as an error occurs.
ErrorID	UDINT	The ErrorID output provides an error code when an error occurs. A list of possible values and notes on troubleshooting can be found in section Error codes.
Busy	BOOL	This output is TRUE as long as the internal ADS communication of the function block is active.
TxBufCount	UDINT	The output TxBufCount indicates whether the internal PLC buffer still contains data bytes that have not yet been sent.
RxBufCount	UDINT	The output RxBufCount can be used to determine whether there are still received data bytes in the internal PLC buffer that have not yet been transferred to the RxBuffer. The application must ensure that the received data is read out of the RxBuffer fast enough.

Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT v3.1.4016	PC or CX (x86, x64)	Tc2_SerialCom