2.1 KiB
2.1 KiB
IBM Logo program
Theorically we only need these instructions to decode the whole program:
- 00E0 (clear screen)
- 1NNN (jump)
- 6XNN (set register VX)
- 7XNN (add value to register VX)
- ANNN (set index register I)
- DXYN (display/draw)
- This is the most involved instruction. It will draw an N pixels tall sprite from the memory location that the I index register is holding to the screen, at the horizontal X coordinate in VX and the Y coordinate in VY. All the pixels that are “on” in the sprite will flip the pixels on the screen that it is drawn to (from left to right, from most to least significant bit). If any pixels on the screen were turned “off” by this, the VF flag register is set to 1. Otherwise, it’s set to 0.
Binary
- 00E0 Clear SCREEN
- A22A Set Register I to 0x22A
- 600C Set Register 0 to 0xC
- 6108 Set Register 1 to 0x8
- D01F Draw
- Register[0] = 0xC
- Register[1] = 0x8
- N ( how tall is the sprite ) = 0xF
- Register[I] = 0x22A
- 7009 Add 0x9 to Register 0 (new value is 0x15)
- A239 Set Register I to 0x239
- D01F Draw
- Register[0] = 0x15
- Register[1] = 0x8
- N ( how tall is the sprite ) = 0xF
- Register[I] = 0x239
- A248 Set Register I to 0x248
- 7008 Add 0x8 to Register 0 (new value is 0x1D)
- D01F Draw
- Register[0] = 0x1D
- Register[1] = 0x8
- N ( how tall is the sprite ) = 0xF
- Register[I] = 0x248
- 7004 Add 0x4 to Register 0 (new value is 0x21)
- A257 Set Register I to 0x257
- D01F Draw
- Register[0] = 0x21
- Register[1] = 0x8
- N ( how tall is the sprite ) = 0xF
- Register[I] = 0x257
- 7008
- A266 Set Register I to 0x266
- D01F Draw
- Register[0] = 0x21
- Register[1] = 0x8
- N ( how tall is the sprite ) = 0xF Register[I] = 0x266
- 7008 Add 0x8 to Register 0 (new value is 0x29)
- A275 Set Register I to 0x275
- D01F Draw
- Register[0] = 0x29
- Register[1] = 0x8
- N ( how tall is the sprite ) = 0xF
- Register[I] = 0x275
- 1228 Set program counter to 0x228
- From this point onwards I think it is sprite data