9 The Disc, File, and Memory Editors

 The *DEDIT, *FEDIT, and *MEDIT commands invoke an interactive hex and
ASCII data editor . The user interface is the same for all of these
commands. All of the editing commands can be invoked in read-only mode,
which allows viewing but not alteration of the data. The display format
for the editor is similar to *DUMP; on each row, the address of the data
is displayed at the left, followed by a number of bytes in hexadecimal
representation, and then the same bytes in ASCII representation. The
number of bytes which are displayed on each row is 16 in 80 column display
modes, and 8 in 40 column modes. The editor cannot be used in 20 column
modes. In the file editor, the address displayed is the offset from the
start of the file. The disc editor displays the absolute sector address,
and the memory editor displays the absolute memory address. The cursor can
be moved about using the cursor keys. The left and right keys move one
byte forwards or backwards, wrapping around to the next line at the edges
of the screen. The up and down keys move forward or backward by one row.
Larger movements up and down are possible using SHIFT or CTRL with the
cursor keys. SHIFT with the up and down keys moves the cursor one
screenfull forward or backwards. CTRL with the up and down keys moves the
cursor to the start or end of the data. The cursor can be moved to the
start or end of the current line by using CTRL with the left or right
keys. The RETURN key moves the cursor to the start of the next line. The
editor starts with the cursor in the hexadecimal data area. It can be
moved to the ASCII data area by pressing SHIFT with the right cursor key ,
and back to the hexadecimal area with SHIFT and the left cursor key . When
in the hexadecimal area, typing hexadecimal symbols will alter the current
byte. In the ASCII area, the code for the character typed is inserted, and
the cursor is moved one place forward. If the editor is in read-only mode,
no alteration is made. The editor has a buffer of 512 bytes of data which
may be modified before it is updated to disc or memory . The buffer is
updated automatically if you move outside the area which it holds, and it
may be copied back at any time by pressing the COPY key. If an attempt is
made to quit the editor while the buffer has not been updated, the editor
will sound the bell, and continue normally . If a second attempt is made
to quit immediately, the editor will then exit. The ESCAPE key is used to
quit the editor. A summary of the keys recognised is given below:

 Key    Normal		    SHIFT       CTRL
 COPY   Update to disc/memory
 ESCAPE Quit editor
 RETURN Start of next line
 LEFT   Backward byte      Hex area       Start of row
 RIGHT  Forward byte       ASCII area     End of row
 UP     Back row           Back screen    Start of data
 DOWN   Forward row        Forward screen End of data