| FCB+00h |
DR |
- |
Drive. 0 for default, 1-16 for A-P.
In DOSPLUS, bit 7 can be set to indicate that the operation should work with subdirectories rather than files.
|
| FCB+01h |
Fn |
- |
Filename, 7-bit ASCII.
The top bits of the filename bytes (usually referred to as F1' to F8') have the following meanings:
| F1'-F4' |
- |
User-defined attributes.
Any program can use them in any way it likes.
The filename in the disc directory has the corresponding bits set.
|
| F5'-F8' |
- |
Interface attributes.
They modify the behaviour of various BDOS functions or indicate error conditions.
In the directory these bits are always zero.
|
|
| FCB+09h |
Tn |
- |
Filetype, 7-bit ASCII.
T1' to T3' have the following meanings:
| T1' |
- |
Read-Only.
|
| T2' |
- |
System (hidden).
System files in user 0 can be opened from other user areas.
|
| T3' |
- |
Archive.
Set if the file has not been changed since it was last copied.
|
|
| FCB+0Ch |
EX |
- |
Set this to 0 when opening a file and then leave it to CP/M.
You can rewind a file by setting EX, RC, S2 and CR to 0.
|
| FCB+0Dh |
S1 |
- |
Reserved. |
| FCB+0Eh |
S2 |
- |
Reserved. |
| FCB+0Fh |
RC |
- |
Set this to 0 when opening a file and then leave it to CP/M.
|
| FCB+10h |
AL |
- |
Image of the second half of the directory entry, containing the file's allocation (which disc blocks it owns).
|
| FCB+20h |
CR |
- |
Current record within extent.
It is usually best to set this to 0 immediately after a file has been opened and then ignore it.
|
| FCB+21h |
Rn |
- |
Random access record number (not CP/M 1).
A 16-bit value in CP/M 2 (with R2 used for overflow);
an 18-bit value in CP/M 3.
|
If you are writing an emulator at BDOS level, you need to be aware of how CP/M uses the bytes EX, S2, and CR.
Some programs (such as the Digital Research linker, LINK.COM) manipulate these bytes to perform "seek" operations in files without using the random-access calls.