The string with the data read from the file. The method also affects the state of fd.laststatus. The following status codes are possible:
0- PL_FD_STATUS_OK: Completed successfully.
1- PL_FD_STATUS_FAIL : Physical flash memory failure (fatal).
2- PL_FD_STATUS_CHECKSUM_ERR: Checksum error has been detected in one of the disk sectors (fatal).
3- PL_FD_STATUS_FORMAT_ERR: Disk formatting error has been detected (fatal).
8- PL_FD_STATUS_NOT_READY: The disk is not mounted.
10- PL_FD_STATUS_NOT_OPENED: No file is currently opened "on" the current value of the fd.filenum property.