FB_FileTell

FB_FileTell 1:

The function block FB_FileTell determines the current position of the file pointer. The position indicates the relative offset from the start of the file.

Note that for files opened in "Append at end of file" mode, the current position is determined by the last I/O operation, not by the position of the next write access. After a read operation, for example, the file pointer is at the position where the next read access will take place, not at the position where the next write access will take place. In append mode, the file pointer is always moved to the end before the write operation.

If no previous I/O operation was performed and the file was opened in append mode, the file pointer is at the start of the file.

	This function block is only suitable for logging in real-time to a limited extent. For good performance, we recommend using the TF3500 TwinCAT Analytics Logger product, which is subject to a charge.

Inputs

VAR_INPUT
    sNetId    : T_AmsNetId;
    hFile     : UINT;
    bExecute  : BOOL;
    tTimeout  : TIME := DEFAULT_ADS_TIMEOUT;
END_VAR

Name	Type	Description
sNetId	T_AmsNetId	String containing the AMS network ID of the target device to which the ADS command is addressed (type: T_AmsNetId).
hFile	UINT	File handle, which was generated when the function block FB_FileOpen was created.
bExecute	BOOL	The function block is activated by a rising edge at this input.
tTimeout	TIME	States the length of the timeout that may not be exceeded by execution of the ADS command.

Outputs

VAR_OUTPUT
    bBusy    : BOOL;
    bError   : BOOL;
    nErrId   : UDINT;
    nSeekPos : DINT;(* On error, nSEEKPOS returns -1 *)
END_VAR

Name	Type	Description
bBusy	BOOL	When the function block is activated, this output is set to TRUE and remains set until feedback is received. As long as bBusy is TRUE, no new command can be executed.
bError	BOOL	If an error occurs during command execution, this output is set, once the bBusy output has been reset.
nErrId	UDINT	Returns the ADS error code or the command-specific error code when the bError output is set.
nSeekPos	DINT	Returns the current position of the file pointer.

Command-specific error code	Possible cause
0x703	Invalid or unknown file handle.
0x70E	File was opened with wrong method (e.g. with obsolete FILEOPEN function block).

Example of calling the function block in FBD:

PROGRAM Test
VAR
    fbFileTell        : FB_FileTell;
    hFile             : UINT;
    bFileTell         : BOOL;
    bFileTellBusy     : BOOL;
    bFileTellError    : BOOL;
    nFileTellErrorId  : UDINT;
    nFileTellSeekPos  : DINT;
END_VAR

Requirements

Development environment	Target system type	PLC libraries to include (Category group)
TwinCAT v3.1.0	PC or CX (x86, x64, ARM)	Tc2_System (System)