I think FB_FileWrite() would do the trick. Beckhoff FB_FileWrite

I use this functionality to log data in a task running at 500uS. Open/Create a file with FB_FileOpen(). Use the same handle for FB_FileWrite() and trigger the execute (it needs an positive flank) each time you want to write data to the file. Keep in mind that the actual accessing of the file takes time depending on your hardware. In our case we write to a SATA harddisk and we had to create a memory buffer for approx. 200ms of data. The access and write time to the file was approx 100ms. In our case we then write the buffer as a large 'chunk' of data at one go into the file. Hope this helps.

Regards

Ludo