For the Spell Book this month a Kentish wizard has sent me the following trick to confuse those trolls who would attempt to copy your game files. This involves saving and loading using filenames made up of the alternative mode 7 character set.

As can be seen from pages 488 and 489 of the User Guide, the letters A - Z appear twice in this character set. This means that either PRINT CHR$(65) or PRINT CHR$(193) will print the character 'A'. Pressing the standard keyboard 'A' character corresponds to CHR$*65) and it is this set which the filing system expects. To save a file called ABC using the alternative letters, use the following:

NAME$ = CHR$(193)+CHR$(194)+CHR$(195)
SAVE NAME$

The file cannot now be reloaded by simply typing LOAD "ABC"

To confuse the trolls, you should ensure that your main adventure program is saved with an alternative filename in this way. The header program should contain a CHAIN command which will appear, when listed, as CHAIN "ABC", or whatever. However, while the characters 'ABC' will be seen as the filename, you should ensure that it is the values of &C1, &C2 and &C3 (decimal 193, 194 and 195), which have been poked into the correct position in the file for 'ABC'.

To achieve this, insert the command CHAIN "ABC" into the header program and then examine the memory using a monitor utility such as Exmon to find the position of the letters (codes &41, &42 and &43 in this case). Using these addresses, change the contents using the ? operator (e.g. ?&0EF0=&C1).