Operating VOYEUR T2.0 (Part 3 of 3)


Another prompt, "Poke", allows the replacement of data in RAM (M100 and T102 addresses above 32767 and T200 addresses above 40959, with full expansion).  With the cursor over the character representing the byte to be replaced, press key "P" for the prompt and then either accept the default byte by pressing only "ENTER", or enter the new byte as a decimal number (0-255) or hex number (0-HFF) or as a non-numeric character.  Numeric characters (digits 0-9 used as strings) must be entered as their ASCII values (48-57).  Immediately following a poke, the default for the next poke will be the same byte, facilitating multiple pokes of a single byte.  Immediately following a search, the default will be the last byte entered at the search prompt, allowing the character under the cursor to be copied by pressing key "S", tapping "ENTER" twice, then moving the cursor to the desired address and pressing key "P" and "ENTER".

Pokes should normally be confined to addresses below MAXRAM (62960 for the M100/T102, 61104 for the T200).  The inveterate time-traveller (specializing in January 1, 1900) may wish to experiment by poking in the operating-system area above MAXRAM.  Even at lower addresses, however, poking requires great care (and backed-up files)!

The most outstanding feature of VOYEUR is its ability, toggled on or off by key "B", to decode BASIC tokens: bytes that represent keywords when a BASIC program is saved as a .BA file.  These tokens constitute much of the "garbage" we are told to discard after recovering data from a cold start.  For bytes used as tokens, the keywords appear on the information line; for other bytes, the characters are duplicated in the same position for easier reading of a sequence.  The decimal line number is also printed in this position.

When copying to a file with BASIC decoding on, the keywords or decimal numbers are sent to the file in place of the bytes (tokens or binary code) representing them.  The 16-bit binary address of the following line, which precedes each binary line number, is omitted.  For the line number, the conversion to decimal is made when the cursor is on the preceding null.  When the cursor is on the other characters representing the number, nothing appears at the keyword position, or is filed, if the cursor is moved from left to right in single steps; for other cursor motions, incorrect translations may appear, such as a keyword for a binary-number byte.

For high 8-bit characters (bytes 128-255) within data strings to not be interpreted as tokens, the quotation mark (") preceding the string will disable the conversion to keywords normally done in BASIC mode.  The conversion is restored by another quotation mark or by the null ending the line.  This should always work correctly while running, but errors can result from moving the cursor manually into or out of a string in a vertical direction, or starting or stopping a scan within a string.  Move once through a quotation mark to correct.

If started at the null preceding the program, without having stepped right from another null, VOYEUR T2.0 can always copy a tokenized (.BA) program to a file as a perfect ASCII (.DO) listing, which can then be loaded as-is except for deleting a CR/LF at the beginning and extraneous material at the end, exactly reconstructing the original .BA file.

With BASIC decoding off, characters which are displayed in reverse video are filed with caret ("^") prefixes if not otherwise displayed by TEXT in this way.

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