Operating VOYEUR N2.0 (Part 2 of 3)


Press key "A" and the "Address" prompt will reappear using the 16-bit binary value (on the info line) less one as the default entry.  Press only the return key to accept the default, or enter any other address in decimal (-65536 to 65535) or hex (0 to HFFFF).  Hexadecimal entries at all prompts must be prefixed by "H" or "h", and upper or lower case letters may be used interchangeably.  Note that the two characters immediately preceding each filename in the directory represent bytes forming the 16-bit binary address of that file; preceding these is a byte representing the type of file (192 for .DO, 128 for .BA, 160 for .CO, or 0 for a dead file).  Place the cursor over this third character in front of the filename, press key "A" and the return key.

After the address is entered, the character for the byte at that address will be displayed under the cursor.  If the address was on the screen, the cursor will move to that position; otherwise it will stay where it was.  Press key "C" to clear the screen and move this character to the upper left corner, then press the return key to scan or keys "F" and "R" to copy, pressing key "B" first if BASIC decoding is desired.  Alternatively, starting the scan without clearing the screen allows a split-screen comparison of different areas of memory.

If the file selected was a BASIC file, the character under the cursor will be the null (0) preceding the first program line.  The two bytes that follow will be the address of the next BASIC program line, and appears as the new sixteen-bit number on the information line which becomes (less 1) the default for the address prompt.  Merely pressing key "A" and the return key will therefore change the address to the null preceding the next BASIC line.  Since the null separating BASIC lines is always followed by the sixteen-bit address of the next line, pressing key "A" and the return key alternately will quickly jump the address from one program line to the next (emulating the method by which BASIC finds the lines for commands such as GOTO).  The jumps can be easily followed since, in BASIC mode, the BASIC line number appears on the info line when the cursor is on the null preceding the BASIC line.

To display other address ranges without using the address prompt, scan or otherwise move the cursor to the end of the character display, at bottom right.  Pressing the return key will then scroll the display and restart the scan for new addresses, with automatic scrolling enabled for successive lines.  Alternatively, pressing key "T" will "turn the page": clearing the screen and restarting the scan with the character for the next address in the upper-left corner.  Pressing key "N" or key "L" will, at any cursor position, change the address to the next or last "page" without moving the cursor, i.e., it jumps by the display size (280 bytes); repeated presses can quickly cover a large range.

The "Search" prompt has been mentioned: for a list of strings, any one of which will halt the scan or a run.  To search for other occurances of the character under the cursor, press key "S" for the prompt and then press the return key only.  Then, or instead, enter one or more bytes in decimal (0-255) or hex (0-HFF), or enter one or more strings of the same length such as individual non-numeric characters.  Non-numeric strings or higher-valued (>255) numeric strings can be entered in bunches of any length, but the length of the string searched for is determined by the length of the last entry.  Enter a dummy non-numeric string to adjust if necessary, e.g., "xxxxx" for a 5-character search.  A reminder of the string length that will be searched for is provided after each entry.  A search for more than one multi-character string will possibly yield "hits" on unwanted sequences formed from adjacent entries; an unlikely dummy string can be entered as a separator if this is a problem.

To search for a string of only numeric characters, or with leading numeric characters, having a value less than 256 (e.g., string "72", not to be interpreted as byte 72, which is character "H"), first enter the string with any non-numeric prefix ("x72") or any numeric prefix or suffix forming a number larger than 255 ("772" or "722"), and then enter a dummy non-numeric string ("xx") equal in length to the original string.  A careful distinction must be made between digits entered this way as string characters, and digits entered as bytes; e.g., character "0", ASCII 48, must be entered as "48" or as "x0" and "x"; byte zero, the null, is entered simply as "0".  Entering "999" causes the entire search list to be cleared, confirmed by "0 byte search?".  Following an entry, the search prompt remains in order to facilitate multiple entries and to display the search string length; terminate by pressing the return key only.  A very long search list may result in an "OS" (out-of-string-space) error, requiring an increase in the size of the "CLEAR255" statement in line 0.