FB_FileRead

With the function block FB_FileRead the contents of an already opened file can be read. Before a read access, the file must have been opened in the corresponding mode. In addition to the FOPEN_MODEREAD, the appropriate format (FOPEN_MODEBINARY or FOPEN_MODETEXT) is also important to achieve the desired result.

	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;
    pReadBuff  : PVOID;
    cbReadLen  : UDINT;
    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.
pReadBuff	PVOID	Address of the buffer into which the data are to be read. The buffer can be a single variable, an array or a structure, whose address can be found with the ADR operator.
cbReadLen	UDINT	Number of bytes to be read
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;
    cbRead : UDINT;    
    bEOF   : BOOL;
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.
cbRead	UDINT	Number of currently read bytes
bEOF	BOOL	This output is set if the end of the file was reached and no further data bytes could be read (cbRead=0). This output is not set if further data bytes could be read (cbRead>0).

Command-specific error code	Possible cause
0x703	Invalid or unknown file handle.
0x70A	No memory for read buffer.
0x70E	File was opened with wrong method (e.g. with obsolete FILEOPEN function block).

Example of calling the block in ST:

File access from the PLC

Example of calling the function block in FBD:

PROGRAM Test
VAR
    fbFileRead        : FB_FileRead;
    hFile             : UINT;
    bFileRead         : BOOL;
    bFileReadBusy     : BOOL;
    bFileReadError    : BOOL;
    nFileReadErrorId  : UDINT;
    nFileReadCount    : UDINT;
    bFileReadEOF      : BOOL;
    fileData          : ARRAY[0..9] OF BYTE;
END_VAR

After a rising edge at bExecute and successful execution of the read instruction the currently read bytes from the file are found in FILEDATA. The parameter cbRead can be used to determine how many bytes were actually read during the last read operation.

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)