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Message: 5796

Author: andrewbroad

Date: 13/04/2006

Subject: JSW pokes (Re: DrUnKeN mAsTeR!!!'s games - Daniel's review)

 

Daniel wrote:

a) "The DrUnKeN mAsTeR!!!" original edition

- There is an invisible item in "They smashed the stairs" (28). I
guess this is a remnant from the original JSW. The item may be
collected by jumping vertically up on the right side of the column
after inserting e.g. POKE 35358,0.

You must have the wrong number there. That POKE affects the code
which performs extra-life colour-cycling, which is unused in the
unpatched JSW game-engine:

{A contains the colour-attribute to be written}
35354: LD HL,#5C00 ; start of secondary attributes-buffer
35357: LD DE,#5C01
35360: LD BC,#1FF ;; 511 bytes to be copied
35363: LD (HL),A ;;; poke the first byte (top-left cell)
35364: LDIR ;;;;;;;; copy it to the rest of the cells
{Every cell in the secondary attributes-buffer now has that colour-
attribute}

The LDIR instruction behaves as follows:
1. copy the byte at the address in HL to the address in DE;
2. HL:= HL + 1;
3. DE:= DE + 1;
4. BC:= BC - 1;
5. if BC is not 0 then repeat Steps 1 to 5.

POKE 35358,0 changes one line of the above code as follows:
35357: LD DE,#5C00
So only the top-left cell gets set. Some cheat! ;-)

I think you mean POKE 36348,60, which lets Willy jump up through
Earth-cells on his left. This POKE alters the following code...

36343: LD A,(#80B2) ; Earth colour-attribute
36346: CP (HL) ;;;;;; compare with cell left above Willy's head
36347: JP Z,36540 ;;; if equal then go to 36540
36350: INC HL ;;;;;;;
36351: CP (HL) ;;;;;; compare with cell right above Willy's head
36352: JP Z,36540 ;;; if equal then go to 36540

...as follows:
36347: JP Z,36412 ;;; if equal then go to 36412

Likewise, POKE 36353,60 lets Willy jump up through Earth-cells on
his right. Both POKEs have nasty side-effects which can cause Willy
to become misaligned and fall through stand-onable cells until he
falls off the bottom of the screen.

--
Dr. Andrew Broad
http://geocities.com/andrewbroad/
http://geocities.com/andrewbroad/spectrum/
http://geocities.com/andrewbroad/spectrum/willy/

 

 

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