APPLICATIONSDISQUE ★ DEDIT ★

Dedit|Computing With the Amstrad)Applications Disque
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DEDIT is a disc editor which will enable you to edit any sector on any track of a disc. If you're careful you'll be able to recover programs that have been accidentally deleted.

To use it to full advantage, we have to consider how the Amstrad disc system works. There are three standard disc formats:

  • System format (CP/M).
  • IBM format (IBM PC CP/M compatible).
  • Data format (for future use).

The formats have two things in common: each has 40 tracks per disc and all of the sectors are 512 bytes in length. The main differences between each format are the number of sectors on a track and the sector numbers.

Here's a list of the sector information for each format:

System format:

  • 9 sectors per track
  • Sector numbers = 65 to 73.

IBM format:

  • 8 sectors per track
  • Sector numbers = 1 to 8.

Data format:

  • 9 sectors per track
  • Sector numbers = 193 to 201.

You don't need to worry about the format of the disc being edited because Dedit will work it out for you. Anyway, let's see how to use it.

Type in Program I and save it. On running the program the Amstrad will change to Mode 2 and draw a large box in the centre of the screen.

You will be asked for the drive is being displayed - 0 if it's the first 256 bytes of the sector and 1 if it's the last 256 bytes. To the left of the page number is the track and sector number of the sector held in memory.

You now have several options open to you. You can either edit the sector in memory, read another section of the disc or write the sector back to the disc.

Table 1 lists all of the commands and control keys. There's a very useful Help page which lists all of the commands. You can display it by pressing 0 on the numeric pad (f0 on the CPC664).

New track/sector options:

SHIFT (cursor right) next sector
SHIFT (cursor left) previous sector
SHIFT (cursor up) forward 1 track
SHIFT (cursor down) back 1 track

Editing coaaands:
(cursor left) right one byte
(cursor right) left one byte
(cursor down) down one line
(cursor up) up one line

Other coammnd keys: (Numeric pad on the CPC 464)
0 (f0 CPC664) Help page
1 (f1 CPC664) New disc paraaeters
2 (f2 CPC664) Page toggle
3 (f3 CPC664) Edit aode hex/ascii
4 (f4 CPCA64) Write sector to disc
5 (f5 CPC664) Exit program

Table I

If at any time a disc error occurs the error message will be printed at the bottom of the screen along with "Retry, Ignore or Cancel".

It's always worth re-trying (R) in case the Amstrad's had a little hiccup. This has occurred several times in the development of Dedit and its cause is still a mystery.
Let's take a typical look at how Dedit should be used.

First of all the disc drive must be selected. In most cases 0 will be entered, indicating that drive A is being used. Next the track and sector numbers are needed. Suppose we enter 2 for the track and 65 for the sector.

The sector will now be loaded and displayed on the screen.

If, however, the sector you selected isn't the one you want to edit you can move to another section of the disc by pressing the appropriate cursor arrow keys while holding down Shift - see Table I for a command summary.

For example, if we pressed (Shift+cursor right) the next sector would be loaded. In our case this would be sector 66 from track 2.

Once the desired sector has been located we can start editing. There are two editing modes, hex and Ascii. Toggle is selected by pressing 3 on the numeric pad (f3 on CPC664).

In hex mode the contents of the sector are altered by entering hexadecimal digits (0-9 and A-F). Note that the numeric pad on the CPC464 should not be used to enter the digits 0-9. Instead use the numeric keys above "QWERTY".

The byte being edited can be changed by moving the editing cursor to the desired byte within the sector. This is achieved by pressing the appropriate cursor arrow keys. 

The other edit option allows you to enter Ascii characters into the sector. For example, if you typed ABCD the bytes &41 ,&42,&43 and &44 would be entered starting from the editing cursor's previous position.

You can tell which editing mode you are in by looking at the editing cursor's position. If it is over the hexadecimal bytes you are in the hex mode, otherwise you're in Ascii mode.

Once you are satisfied that the sector has been successfully changed you must write the sector back to the disc. This is done by pressing 4 on the keypad (f4 on the CPC664), after which you will be prompted with "Are you sure Y/N?"

If you want to write the sector back to disc press Y. Pressing N aborts the operation and returns you to the editing mode.

Now it's time for you to discover how your Amstrad stores information on the disc. Happy hunting!

CWTA

★ PUBLISHER: Computing with the Amstrad
★ YEAR: 1985
★ CONFIG: 64K + AMSDOS
★ LANGUAGE:
★ AUTHOR: Ches Jeske

★ AMSTRAD CPC ★ DOWNLOAD ★

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L'Amstrad CPC est une machine 8 bits à base d'un Z80 à 4MHz. Le premier de la gamme fut le CPC 464 en 1984, équipé d'un lecteur de cassettes intégré il se plaçait en concurrent  du Commodore C64 beaucoup plus compliqué à utiliser et plus cher. Ce fut un réel succès et sorti cette même années le CPC 664 équipé d'un lecteur de disquettes trois pouces intégré. Sa vie fut de courte durée puisqu'en 1985 il fut remplacé par le CPC 6128 qui était plus compact, plus soigné et surtout qui avait 128Ko de RAM au lieu de 64Ko.