Disk Doctor
With this program, you can physically work on your disks for
the VZ200 and VZ300 computers.

You can directly read each sector on the disk, have it 
displayed in hexidecimal, make modifications and write it 
back to disk.
Allows any checksum errors on the disk to be ammended, as
long as there is no physical damage to the magnetic layer,
by reading the defective sector and then writing it back
correctly.

Operating directions
The program is loaded from disk and run with BRUN"DOC".
After correctly loading, a title screen appears, which
requests from you the address details necessary to read the
first sector.

Drive (1/2)
Select the desired drive by entering "1" or "2".

Track(00-27)
Enter the desired track on the disk in hexadecimal notation.
Two digits must always be entered eg, 0F and not just F.

Sector(0-F)
Enter in hexidecimal the sector to be addressed on the track 
selected above.
Each time the permissable value range is given in brackets.
All other input except this, CTRL-BREAK and "Q" will be 
ignored.

Entering "Q", instead of the input outlined above, will end
the program and reinitalise the computer.
Simultaneously pressing of "CTRL" and "BREAK" at any point 
will result in a restart, and the title screen will again
appear. You must, for example, use this method if you wish 
to change to the other disk drive.
Correctly enter all address values for a sector and it will
be read from the disk and displayed on the screen.

This display is made up as follows:
In the left three columns, the track and sector numbers are 
given in hexidecimal.
On the right next to them are the relative sector addresses,
two digits hexidecimal numbers from 00 to 78. These always 
refer to the first byte of each line. Each eight bytes of
the sector is listed in hexidecimal notation, in two four
byte blocks per line.
In the right hand eight columns there follows the ASCII
equivalent of these eight bytes. Those ASCII codes not able
to be displayed are replaced by "."

+ or RETURN - Move forward ie, the next sector on the disk 
will be read and displayed.

-           - Move backwards ie. the previous sector on the 
disk will be read.

A           - New track ans sector address. You will be asked 
to enter the TRACK and SECTOR again.

M           - Make changes in the MODIFY mode. You can alter
the sector contents and then write the sector back to disk.

CTRL BREAK  - Restart the program.

Q           - Quit the progam.

When reading a sector you can encounter the following errors:

SECTOR NOT ADDRESSES
Address data marks of the addressed sector cannot be found on 
the disk.
After pressing the RETURN key the program returns to the track 
and sector selection.

CHECKSUM ERROR ENCOUNTERED
During reading of the sector a checksum error is detected in 
the data field of the sector. After pressing RETURN the
sector contents will be displayed and can then be worked on.
When this sector is written back the checksum will be 
automatically corrected.

Operating directions in MODIFY mode.
When you have the sector display, press the M key to change
the program to the MODIFY mode.
It is recognisable, in that one of the displayed digits in the
sector contents flashes.
In this mode you can alter the sector contents and write the 
sector back to disk.

The following operating functions are at your disposal.

Arrow keys (+CTRL) - With these you can position the 
flashing cursor to the desired place in the data field of
the sector.

0-F   - Pressing one of these keys alters the sector contents
in the internal buffer. The ASCII display on the right side is
automatically altered with it.

Q     - Pressing Q returns you to the display mode, all 
alterations to the sector will be cancelled.

CTRL-BREAK  - Restarts the program.

RETURN  - Write the sector back to disk.
You will be asked next if all alterations are correct. The
"Y" key will write the sector to disk. Pressing the "N"
will return you to the MODIFY mode. After a sector is written
to disk, it will, on completion, be shown on the screen in the
display mode.
By entering a new address or by stepping forwards or
backwards, another sector can be displayed.
When writing a sector, just as when reading, an error can
occur, where the address of a sector isn't found. In such
cases, an error message is displayed. After pressing RETURN
another attempt will be made to read the sector.