add cheat for Up'n Down

res/history.md

@@ -9,7 +9,7 @@
 
  - Added help screen (press ? in search or browse mode to show)
  - Added global cheat mode (press Ctrl-C in search or browse mode to toggle)
- - Added 49 game cheats
+ - Added 50 game cheats
  - Fixed corrupted graphics in Asteroid Blaster
  - Fixed corrupted graphics in Sneakers game, demo, and screenshots, and now we are entirely done with this I promise
  - Added missing levels in Out Of This World

src/prelaunch/up.n.down.a

@@ -0,0 +1,23 @@
+;license:MIT
+;(c) 2019 by 4am
+
+!cpu 6502
+!to "build/PRELAUNCH/UP.N.DOWN",plain
+*=$106
+
+         !source "src/prelaunch/common.a"
+
+         ldx   #7         ; copy patch code to zero page (stack will be destroyed by the time we need to patch)
+-        lda   patch,x
+         sta   $F8,x
+         dex
+         bpl   -
+         lda   #$F8       ; call patch instead of $200
+         sta   $4061
+         lda   #$00
+         sta   $4062
+         jmp   $2DC2
+patch
+         lda   #$B5
+         sta   $0912      ; patch - don't decrease lives
+         jmp   $0200      ; continue with load