The Programmer's Guide to TRSDOS Version 6 - Tim Mann's Home ...

Bit 3 Specifies the visibility; if "1", the file is INVisible to a DIRectory
display or other library function where visibility is a parameter. If a "0",
then the file is declared VISible.
Bits 0-2 Contain the access protection level of the file. The 3-bit binary value is
encoded as follows:
0 - FULL 1 - REMOVE 2 - RENAME 3 - WRITE
4 - UPDATE 5 - READ 6 - EXEC 7 - NO ACCESS
5.4.2 FLAG FIELD -
This field contains four file flags in bits 7-4. The low-order nibble is associated with
the DATE field. The flags are encoded as follows:
Bit 7 When this bit is set, the system will be kept from deallocating any unused
space at the end of the file when the file is closed. This bit will be set
to a "1" if the file was "CREATEd" by the DOS library command, CREATE. Such
a file will never shrink in size. The file will remain as large as its
largest allocation.
Bit 6 This flag is termed the "MOD flag". If this flag is set to a "1", it
indicates that the file has not been backed up since its last modification.
The BACKUP utility is the only DOS facility that will reset this flag. It is
set during the file close operation if the File Control Block (FCB+0, Bit 2)
indicated a modification of file data.
Bit 5 This bit is set by the system when a file is opened with UPDATE or greater
access. It is used to detect the presence of an open file for subsequent
OPENs of the same file. The bit is reset by the CLOSE operation.
Bit 4 This bit is used internally by the system.
If the ATTRIBUTE field identifies the record as an FXDE, then this entire byte (flags and
month) will contain the Directory Entry Code of the directory entry forward linked to
this one. This entry is the backward link.
5.4.3 MODIFICATION DATE -
This field is composed of 12 bits, the low-order nibble of DIR+1 and the entire byte of
DIR+2. It contains the month, day, and year for the day that the file was last modified.
The field is encoded as follows.
Bits 11-8 Contain the binary month of the last modification date. If this field
is a zero, the system date was not set when the file was established
nor since if it was updated.
Bits 7-3 Contain the binary day of last modification.
Bits 2-0 Contain the binary YEAR - 1980. That is to say that 1980 would be
coded as 000, 1981 as 001, 1982 as 010, etc.
5.4.4 EOF OFFSET -
This field contains the end-of-file offset byte. It points to the position in the ending
sector of where the next byte can be placed. If EOF OFFSET is a zero, it means that a
full sector of 256 bytes had been written to the last sector of the file and the next
byte must be written to a new sector. This byte, and the ending record number (ERN), form
a triad pointer to the byte position immediately following the last byte written.
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