JSW Teleporter overlay

A JetSet Willy module enabling teleportation between rooms

Click here to download the module (76 bytes).

The teleportation module is a small overlay file that can be placed in JetSet Willy (either 48k or 128k versions) allowing teleportation between rooms. It requires at least 80 contiguous bytes of memory.

The first thing to do is to choose the address at which to load TELEPORT.

In the 48k versions, a good place is an unused room - say "[" or room 63.
In the 128k versions, more memory is available and (in version 0.00HL3) there is a memory map which can be used to locate spare memory. In the map, the identity 61h is reserved for this module.

The next step is to modify the file to reflect the actual load address used, and to set up the transporters. The exact method used depends on whether you are using an emulator or a real Spectrum, but:

Suppose the module is to be loaded at "base". Then at "base+5" is a 16-bit address pointing to a data area - normally "base+4Ah".
At "base+4Ah" there is a zero byte. This byte should be set to the number of teleporters in the game. There should then follow a list of entries - four bytes for each teleporter:

     DB       room                ;Room with the teleporter in
     DB       y                   ;Y-coordinate. 0 is the top of the room
                                  ;                and 255 is the bottom
     DB       x                   ;X-coordinate. 0 is the left-hand side of
                                  ;                the room and 31 is the
                                  ;                right-hand side.
     DB       dest                ;The destination room into which Willy will
                                  ;be transported.

For example, the byte sequence 21h,30h,1Ch,00h means that Willy will be transported from the right-hand end of the top platform in the Bathroom to the Off-License (where he will invariably die, since he appears on top of a guardian :-) )

Once you have created your final overlay, you have to insert it into the game.

If your game is on a tape, disc or TAP file, then this is easy. Insert the following line in the BASIC loader just before the RANDOMIZE USR line (or the PAUSE line for +3 disc versions):

     LOAD "TEL.JS2" CODE base : POKE 35696, 205: POKE 35697, baselow:
                                POKE 35698, basehigh

If your game is stored as a snapshot, then use Z80 v3. Start by using its "load memory block" feature to bring the overlay into memory; then activate the emulated Multiface 128. Use it to POKE the bytes

       0CDh baselow basehigh

into memory at 8B70h.

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