Short summary

Name	`System_read`
→POU type	→function
Category	more system blocks, blocks for calling system functions, block with internal error diagnostic
Graphical interface
Available since	version 1.13.0 (for logi.CAD 3) and version 2.3.901 of the →runtime system – initial variant: `data` as `VAR_INPUT` This block is supported for →Raspberry Pi only. version 1.54.0 (for logi.CAD 3) and version 3.0.9 of the →runtime system – enhancement: additional output `rc`, `data` as `VAR_IN_OUT` This block is supported for the built-in PLC and for Raspberry Pi only. version 1.109.0 (for logi.CAD 3) and version 3.19.0 of the →runtime system This block is supported for the built-in PLC , for Raspberry Pi and when using the platform `LinuxX86` only. version 2.0.4 (for library `System`) and version 3.23.0 of the →runtime system This block is supported for the built-in PLC and when using the platform `LinuxX86` . Moreover, the block is supported when using the following target systems: Raspberry Pi, →phyBOARD-Regor, →phyBOARD-Wega, →µMIC.200 version 2.0.5 (for library `Standard`) – graphical interface with in-out variable

Functionality

The block reads up to 64 bytes from a given file descriptor.

Required expertise

In order to use this block efficiently, you have to be familiar with the functionality of the underlying system call for the operating system used on the PLC.

Inputs, outputs, return value

	Identifier	→Data type	Description
Inputs:	`fd`	`DINT`	the file descriptor
Inputs:	`count`	`DINT`	number of bytes to read in one go
In-outs (VAR_IN_OUT):	`data`	`ARRAY[0..63] OF BYTE`	the read bytes
Outputs:	`rc`	`DINT`	return code: `0` = no error `-2` = invalid number of bytes `-3` = failed system call
Outputs:	`errno`	`DINT`	error code returned by the system call Windows standard values (valid for built-in PLC): see https://msdn.microsoft.com/en-us/library/t3ayayh1.aspx Linux standard values (e.g. valid for Raspberry Pi): see http://www-numi.fnal.gov/offline_software/srt_public_context/WebDocs/Errors/unix_system_errors.html
Return value:	–	`LINT`	returns the return code of the read system call

Input EN and output ENO are available when →calling the block. See "Execution control: EN, ENO" for information on input EN and output ENO.

See:

"Blocks for safe logic" whether this block is supported for developing safety-relevant applications.
"Highlighting safe logic in the FBD-editor" for the effects when using the block as a block for safe logic .

The output ENO of this block will only be value TRUE (or an equivalent), in case the given number of bytes has been read.

Internal error diagnostic for block

The block checks the following error cases:

The system service has not been loaded.
The return value of the block is a negative value.
The return code of the function call equates to an error (output rc ≠ value 0).

In such an error case, the output ENO of the block is set to value FALSE (or an equivalent).

Example for usage within ST-editor

At present, there is no example.

When creating your application within the ST-editor, enter a call of a block by typing the text as requested by the syntax or use Content Assist.