Atari 400 Technical Reference Manual page 80

bit 7
=
1 if the file has been deleted.
bit 6
=
1 if the file is in use.
bit 5
=
1 if the file is locked.
bit 0
=
1 if OPEN output.
The flag byte can take on the following values:
$00 = entry not yet used (no file>.
$40
=
entry in use (normal CLOSEd file>.
$41
=
entry in use (OPEN output file>.
$60
=
entry in use (locked file>.
$80
=
entry available <prior file deleted >.
Sector count is the number of sectors comprising the file.
FHS File Sector Format
The format of a sector in your data file is shown below:
Figure 5-17
7
o
+-+-+-+-+-+-+-+-+
data +0
=
=
+-+-+-+-+-+-+-+-+
t f i l e . thi: +125
+-+-+-+-+-+-+ +
Iforward pointerl +126
+-+-+-+-+-+-+-+-+
IS: byte count +127
+-+-+-+-+-+-+-+-+
File Management Subsystem File Sector Format
The FHS uses the f i l e . to verify file integrity. The f i l e .
is a redundant piece of information. The file number! field
contains the value of the directory position of that file. If a
mismatch occurs between the file's
director~
position, and the
file number as contained in each sector, then the DFM will
generate the error $A4.
The forward pointer field contains the 10-bit value for the
diskette sector number of the next sector of the file. The
pointer equals zero for the last sector of a file.
The S bit indicates whether or not the sector is a "short sector"
(a sector containing fewer than 125 data bytes). S is equal to
1 when the sector is short.
OPERATING SYSTEM C016555 -- Section 5
95