3964R

The function block P3964R handles the 3964R protocol. The background communication, which is handled by a separate function block SerialLineControl decides on the hardware interface used. The associated data buffers TxBuffer and RxBuffer (of type ComBuffer) are transferred to the function block P3964R.

Sending

Send data are entered into the send data buffer TXdata by the PLC. The number of data bytes entered is passed on in TXcount, and then TXstart is set to TRUE. While sending, TXbusy=TRUE. Once the data has been successfully transferred, TXready=TRUE.

Receiving

RXstart is set to TRUE to receive data. After a complete data set has been received, the RXready output goes TRUE and RXcount data bytes are ready in the receive data buffer RXdata. While receiving, RXbusy=TRUE.

Interrupt reception

The function block P3964R can be used in either send or receive mode. It is worthwhile switching the function block to receive when transmission is not taking place. As long as the function block is in receive mode, but no start character has been received from the remote terminal, a rising edge at TXstart can interrupt the reception and initiate the sending of data. After the transfer the function block goes into its initial state (Busy=FALSE), and is only switched over to receive by a new edge at RXstart.

Priority

In a 3964R data connection, each remote terminal may send at any time. If both ends attempt to send at the same time, there is a collision. In that case, the end with the lower priority goes into receive mode, while the end with the higher priority sends again. For this reason, when priority is low the output RXready=TRUE, even though data are to be sent. The data in RXdata may then require evaluation. The setting of the priority at the two ends is to be agreed.

Inputs

VAR_INPUT
  TXstart  : BOOL;    (* start signal, edge-triggered *)
  RXstart  : BOOL;    (* start signal, edge-triggered *)
  Priority : BOOL;    (* 3964 priority, TRUE=high, FALSE=low *)
  TXcount  : INT;     (* number of data bytes in TxData *)
END_VAR

Name	Type	Description
TXstart	BOOL	`TXstart` is edge-triggered, so that before a new attempt to send is made, the function block must be called with `TXstart=FALSE`. If `TXstart` is then set to TRUE, this starts the transmission attempt.
RXstart	BOOL	`RXstart` is edge-triggered. `RXstart` is set to TRUE to receive data.
Priority	BOOL	In a 3964R data connection, each remote terminal may send at any time. If both ends attempt to send at the same time, there is a collision. In that case, the end with the lower priority goes into receive mode, while the end with the higher priority sends again. For this reason, when priority is low the output `RXready=TRUE`, even though data are to be sent. The data in `RXdata` may then require evaluation. The setting of the priority at the two ends is to be agreed.
TXcount	INT	The entered number of data bytes is transferred to `TXcount`.

Inputs/outputs

VAR_IN_OUT
  TXdata          : P3964buffer;  (* application data (to send)*)
  RXdata          : P3964buffer;  (* application data (received)*)
  TxBuffer        : ComBuffer;    (* buffer between protocol software and terminal *)
  RxBuffer        : ComBuffer;    (* buffer between protocol software and terminal *)
END_VAR

Name	Type	Description
TXdata	P3964buffer	Send data are entered into the send data buffer `TXdata` by the PLC.
RXdata	P3964buffer	`RXcount` data bytes are available in the receive data buffer `RXdata`.
TxBuffer	ComBuffer	Buffer with send data for the serial hardware being used.
RxBuffer	ComBuffer	Buffer into which received data is placed.

Outputs

VAR_OUTPUT
  Busy       : BOOL;           (* block is active *)
  TXbusy     : BOOL;           (* send state *)
  TXready    : BOOL;           (* send completed, data were transferred *)
  RXbusy     : BOOL;           (* receive state *)
  RXready    : BOOL;           (* receive completed, data were transferred *)
  RXcount    : INT;            (* number of data bytes in RxData *)
  Error      : BOOL;           (* error *)
  ErrorID    : P3964R_Error_t; (* error id *)
  ErrorState : STRING(80);     (* internal error state *)
END_VAR

Name	Type	Description
Busy	BOOL	After the transfer, the function block switches to the basic state (`Busy=FALSE`).
TXbusy	BOOL	While sending, `TXbusy=TRUE`.
TXready	BOOL	Once the data has been successfully transferred, `TXready=TRUE`.
RXbusy	BOOL	While receiving, `RXbusy=TRUE`.
RXready	BOOL	After a complete data set has been received, the output is `RXready=TRUE`.
RXcount	INT	`RXcount` data bytes are available in the receive data buffer `RXdata`.
Error	BOOL	In the event of an error, the output is `Error=TRUE` and the function block goes into the initial state (`Busy=FALSE`).
ErrorID	P3964R_Error_t	The `ErrorID` returns the error code.
ErrorState	STRING	`ErrorState` provides information about the state in which the error occurred when the internal protocol structure is known.

Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT v3.1.4012	PC or CX (ARM, x86, x64)	Tc2_SerialCom