NES Wheel of Fortune game mechanics and assembly documentation.

Addresses related to puzzle selection and RNG

Key inputs (NES standard):
KeyHex value


What the below does: Random stuff. Note that, as far as is known, addresses 0x341, 0x381, 0x3A1, 0x3A2 are always 0 when this is executed. Not all values are possible, even if all possible inputs (0x20-0x22) are entered.
When on the screen showing the round, carry is always set at execution of 00:87F8, and the game polls all inputs 0x20-0x22. When on the spin screen, carry is always clear at execution of 00:87F8, and the game only polls input from 0x22 (0x20 and 0x21 are set to zero).
00:8C4C:E6 0A     INC $000A
;(carry is set on screen showing round; carry is clear when on spin screen)
00:87F8:A5 0B     LDA $000B
00:87FA:65 20     ADC $0020
00:87FC:65 22     ADC $0022
00:87FE:65 21     ADC $0021
00:8800:65 0A     ADC $000A
00:8802:2A        ROL
00:8803:2A        ROL
00:8804:2A        ROL
00:8805:6D A2 03  ADC $03A2
00:8808:4D 41 03  EOR $0341
00:880B:85 0B     STA $000B
00:880D:69 09     ADC #$09
00:880F:65 0C     ADC $000C
00:8811:6D 81 03  ADC $0381
00:8814:49 07     EOR #$07
00:8816:65 0A     ADC $000A
00:8818:65 20     ADC $0020
00:881A:ED A1 03  SBC $03A1
00:881D:85 0C     STA $000C
00:881F:60        RTS

Puzzle selection routines

What the below does: A puzzle selection subroutine, which also messes with the RNG. It is as follows: Let X be a random multiple of 4 from 0 to 0x7C, and add a random number from 0 to 3 if it is not 0x74, 0x78, or 0x7C. Let Y be a random number from 0 to 7. Then take the (Y+1)th high-end bit of address 0x780+X. If it is 0, turn the 0 bit to 1 (this selects a puzzle) and return success (0). If it is 1, return failure (1).
Address 0x17 starts at 8. Each time failure is returned, 0x17 is decremented and the subroutine is called again. This subroutine executes up to 8 times.
04:8006:A5 0B     LDA $000B
04:8008:0A        ASL
04:8009:0A        ASL
04:800A:45 0C     EOR $000C
04:800C:85 0B     STA $000B
04:800E:45 0A     EOR $000A
04:8010:65 0B     ADC $000B
04:8012:85 0C     STA $000C
04:8014:A5 0B     LDA $000B
04:8016:29 7C     AND #$7C
04:8018:AA        TAX
04:8019:C9 74     CMP #$74
04:801B:B0 0E     BCS $802B
04:801D:A5 0C     LDA $000C
04:801F:45 0B     EOR $000B
04:8021:4A        LSR
04:8022:4A        LSR
04:8023:29 03     AND #$03
04:8025:85 1A     STA $001A
04:8027:8A        TXA
04:8028:05 1A     ORA $001A
04:802A:AA        TAX
04:802B:A5 0C     LDA $000C
04:802D:45 17     EOR $0017
04:802F:29 07     AND #$07
04:8031:85 1A     STA $001A
04:8033:A8        TAY
04:8034:BD 80 07  LDA $0780,X
04:8037:39 5D 80  AND $805D,Y
04:803A:F0 03     BEQ $803F
04:803C:A9 01     LDA #$01
04:803E:60        RTS -----
04:803F:BD 80 07  LDA $0780,X
04:8042:19 5D 80  ORA $805D,Y
04:8045:9D 80 07  STA $0780,X
04:8048:8A        TXA
04:8049:4A        LSR
04:804A:4A        LSR
04:804B:4A        LSR
04:804C:4A        LSR
04:804D:4A        LSR
04:804E:85 19     STA $0019
04:8050:E6 19     INC $0019
04:8052:8A        TXA
04:8053:0A        ASL
04:8054:0A        ASL
04:8055:0A        ASL
04:8056:05 1A     ORA $001A
04:8058:85 18     STA $0018
04:805A:A9 00     LDA #$00
04:805C:60        RTS --------

;(data table used above)
04:805D:80 40 20 10 08 04 02 01
Puzzle selection routine:
What the below does: If all bytes of 0x780-0x7FC are 0xFF, turn them all to 0.
04:8065:A2 7C     LDX #$7C
04:8067:BD 80 07  LDA $0780,X
04:806A:C9 FF     CMP #$FF
04:806C:D0 0E     BNE $807C
04:806E:CA        DEX
04:806F:10 F6     BPL $8067
04:8071:A9 00     LDA #$00
04:8073:E8        INX
04:8074:9D 80 07  STA $0780,X
04:8077:E8        INX
04:8078:E0 7E     CPX #$7E
04:807A:D0 F8     BNE $8074
What the below does: Address 0x17 starts at 8 and the subroutine at 04:8006 executed. Each time failure is returned, 0x17 is decremented and the subroutine is called again. This subroutine executes up to 8 times. If at any time the subroutine returns success, then a bit in the range 0x780-0x7FC has been turned from 0 to 1 (a puzzle has been selected).
04:807C:A9 08     LDA #$08
04:807E:85 17     STA $0017
04:8080:20 06 80  JSR $8006
04:8083:F0 42     BEQ $80C7
04:8085:C6 17     DEC $0017
04:8087:D0 F7     BNE $8080
What the below does: If it still returns failure after 8 times, then take the last value of X (from description above), and let Z be the largest multiple of 32 less than X. Starting from address 0x780+Z, take the first byte that is not 0xFF (that means a puzzle is available there). If it reaches address 0x7FC and that byte is 0xFF, then go back to 0x700 and keep trying.
04:8089:A5 0B     LDA $000B
04:808B:29 7C     AND #$7C
04:808D:AA        TAX
04:808E:BD 80 07  LDA $0780,X
04:8091:C9 FF     CMP #$FF
04:8093:D0 09     BNE $809E
04:8095:E8        INX
04:8096:E0 7D     CPX #$7D
04:8098:D0 F4     BNE $808E
04:809A:A2 00     LDX #$00
04:809C:F0 F0     BEQ $808E
04:809E:85 14     STA $0014
04:80A0:8A        TXA
04:80A1:4A        LSR
04:80A2:4A        LSR
04:80A3:4A        LSR
04:80A4:4A        LSR
04:80A5:4A        LSR
04:80A6:85 19     STA $0019
04:80A8:E6 19     INC $0019
04:80AA:8A        TXA
04:80AB:0A        ASL
04:80AC:0A        ASL
04:80AD:0A        ASL
04:80AE:85 18     STA $0018
What the below does: From the above byte which is not 0xFF, take the first high-end bit that is 0. Turn the 0 to 1 (this selects a puzzle).
04:80B0:A9 80     LDA #$80
04:80B2:85 15     STA $0015
04:80B4:06 14     ASL $0014
04:80B6:90 07     BCC $80BF
04:80B8:E6 18     INC $0018
04:80BA:46 15     LSR $0015
04:80BC:4C B4 80  JMP $80B4
04:80BF:BD 80 07  LDA $0780,X
04:80C2:05 15     ORA $0015
04:80C4:9D 80 07  STA $0780,X

ROM bank of puzzles

All pointers are 2-byte little-endian values to NES addresses (04:xxxx range). For example, the hex string "EC 81" points to the address 04:81EC.
Note: The last puzzle (1001st puzzle/puzzle #1000) at 04:C5F5-C607 (ROM 14605-14617) can never be called by the game's puzzle selection routine.
Puzzles are stored in a modified ASCII form:
SymbolHex value
As well, the following rules apply to indicate new line or end of puzzle:
For example, the following string is WHEEL@OF@FORTUNE (@ meaning newline):
57 48 45 45 CC 4F C6 46 4F 52 54 55 CE C5
W  H  E  E  L@ O  F@ F  O  R  T  U  N  E

Addresses related to spin mechanics

Spin mechanics

The spin for speed-up round uses the following randomization rules, in this order:
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GameResources/NES/WheelOfFortune last edited by FractalFusion on 11/10/2013 6:00 AM
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