FB_StringRingBuffer

The function block FB_StringRingBuffer can be used to write string variables into the ring buffer or read previously written string variables from the ring buffer. The written strings are read out according to the FIFO principle in the same order in which they were previously written to the ring buffer. This means that the oldest entries are the first ones that are read. The buffer memory is made available to the function block via the pBuffer/cbBuffer input variables. Writing/reading of strings is controlled via action calls. The function block features the following tasks:

A_AddTail (writes a new string into the ring buffer.)
A_GetHead (reads the oldest string in the ring buffer, but does not remove it.)
A_RemoveHead (reads and removes the oldest string from the ring buffer.)
A_Reset (deletes all strings from the ring buffer.)

Inputs

VAR_INPUT
    bOverwrite : BOOL;
    putValue   : T_MaxString := '';
    pBuffer    : POINTER TO BYTE;
    cbBuffer   : UDINT;
END_VAR

Name	Type	Description
bOverwrite	BOOL	If TRUE and in the event of a buffer overflow the oldest entries are overwritten. If FALSE an error is reported in the event of a buffer overflow (bOk = FALSE).
putValue	T_MaxString	String to be written into the ring buffer.
pBuffer	BYTE	Address of a PLC variables (e.g. ARRAY[...] OF BYTES) to be used as buffer memory by the function block. The address can be determined with the ADR operator.
cbBuffer	UDINT	Max. byte size of the PLC variable to be used as buffer memory. The size can be determined with the SIZEOF operator.

Outputs

VAR_OUTPUT
    bOk      : BOOL;
    getValue : T_MaxString := '';
    nCount   : UDINT;
    cbSize   : UDINT;
END_VAR

Name	Type	Description
bOk	BOOL	Returns TRUE, if a new string was added or removed successfully. Returns FALSE in the event of a buffer overflow or if no more entries are available in the buffer.
getValue	T_MaxString	This output returns the last string that was read from the ring buffer.
nCount	UDINT	Returns the current number of buffered strings.
cbSize	UDINT	Returns the current number of assigned data bytes in the buffer. The number of assigned data bytes is always greater than the actual number of written value data. Each string is complemented with additional information, so that it can be located later.

Requirements

Development environment	Target platform	PLC libraries to be integrated (category group)
TwinCAT v3.1.0	PC or CX (x86, x64, ARM)	Tc2_Utilities (System)