Stella (Atari 2600 Hardware)
On the web: Stella Programmer's Guide
The address decoding for the 2600 is very simple. The TIA is accessed if A12 is 0 and A7 is 0. The TIA is selected if (address&1080 == 0000).
The TIA chip uses the 6 lower address lines A0-A5. The reads seem to ignore A4 and A5.
The addresses have different read/write definitions and many of them are strobes that are triggered by writing any value.
Note that the 6502 has an 8-bit stack pointer. The CPU automatically sets the upper byte of the address to 01. The RIOT chip RAM ghosts from 00xx to 01xx putting the stack in RAM.
TIA (read)
| 0000r | CXM0P | XX...... Collisions D7=M0/P1, D6=M0/P0 |
| 0001r | CXM1P | XX...... Collisions D7=M1/P0, D6=M1/P1 |
| 0002r | CXP0FB | XX...... Collisions D7=P0/PF, D6=P0/BL |
| 0003r | CXP1FB | XX...... Collisions D7=P1/PF, D6=P1/BL |
| 0004r | CXM0FB | XX...... Collisions D7=M0/PF, D6=M0/BL |
| 0005r | CXM1FB | XX...... Collisions D7=M1/PF, D6=M1/BL |
| 0006r | CXBLPF | X....... Collisions D7=BL/PF |
| 0007r | CXPPMM | XX...... Collisions D7=P0/P1, D6=M0/M1 |
| 0008r | INPT0 | X....... Paddle input 0 |
| 0009r | INPT1 | X....... Paddle input 1 |
| 000Ar | INPT2 | X....... Paddle input 2 |
| 000Br | INPT3 | X....... Paddle input 3 |
| 000Cr | INPT4 | X....... Latched inputs (joystick buttons) |
| 000Dr | INPT5 | X....... Latched inputs (joystick buttons) |
TIA (write)
| 0000w | VSYNC | ......X. D1=1 starts the vertical sync |
| 0001w | VBLANK | XX....X. D1=1 starts the vertical blank (D6 and D7 config INPT0-5) |
| 0002w | WSYNC | strobe Halts processor until leading edge of horizontal blank |
| 0003w | RSYNC | strobe Resets sync counter (used in chip testing) |
| 0004w | NUSIZ0 | ..XXXXXX Number and size of player/missile P0 |
| 0005w | NUSIZ1 | ..XXXXXX Number and size of player/missile P0 |
| 0006w | COLUP0 | XXXXXXX. Color-luminance of player 0 |
| 0007w | COLUP1 | XXXXXXX. Color-luminance of player 1 |
| 0008w | COLUPF | XXXXXXX. Color-luminance of play filed |
| 0009w | COLUBK | XXXXXXX. Color-luminance of background |
| 000Aw | CTRLPF | ..XX.XXX Control playfield, priorities, and ball size |
| 000Bw | REFP0 | ....X... D3=1 reflects player 0 |
| 000Cw | PEFP1 | ....X... D3=1 reflects player 1 |
| 000Dw | PF0 | XXXX.... Playfield 0 bits (upper 4 bits) |
| 000Ew | PF1 | XXXXXXXX Playfield 1 bits |
| 000Fw | PF2 | XXXXXXXX Playfield 2 bits |
| 0010w | RESP0 | strobe Set horizontal position of player 0 |
| 0011w | RESP1 | strobe Set horizontal position of player 1 |
| 0012w | RESM0 | strobe Set horizontal position of missile 0 |
| 0013w | RESM1 | strobe Set horizontal position of missile 1 |
| 0014w | RESBL | strobe Set horizontal position of ball |
| 0015w | AUDC0 | ....XXXX Noise, tone, division control channel 0 |
| 0016w | AUDC1 | ...XXXXX Noise, tone, division control channel 1 |
| 0017w | AUDF0 | ...XXXXX Frequency divider channel 0 |
| 0018w | AUDF1 | ....XXXX Frequency divider channel 1 |
| 0019w | AUDV0 | ....XXXX Volume channel 0 |
| 001Aw | AUDV1 | ....XXXX Volume channel 1 |
| 001Bw | GRP0 | XXXXXXXX Player 0 graphics |
| 001Cw | GRP1 | XXXXXXXX Player 1 graphics |
| 001Dw | ENAM0 | ......X. D1=1 to enable missile 0 |
| 001Ew | ENAM1 | ......X. D1=1 to enable missile 1 |
| 001Fw | ENABL | ......X. D1=1 to enable ball |
| 0020w | HMP0 | XXXX.... Horizontal motion offset for player 0 |
| 0021w | HMP1 | XXXX.... Horizontal motion offset for player 1 |
| 0022w | HMM0 | XXXX.... Horizontal motion offset for missile 0 |
| 0023w | HMM1 | XXXX.... Horizontal motion offset for missile 1 |
| 0024w | HMBL | XXXX.... Horizontal motion offset for ball |
| 0025w | VDELP0 | .......X D0=1 to delay player 0 one vertical line |
| 0026w | VDELP1 | .......X D0=1 to delay player 1 one vertical line |
| 0027w | VDELBL | .......X D0=1 to delay ball one vertical line |
| 0028w | RESMP0 | ......X. D1=1 to reset missile 0 to player 0 |
| 0029w | RESMP1 | ......X. D1=1 to reset missile 1 to player 1 |
| 002Aw | HMOVE | strobe Executes horizontal motions |
| 002Bw | HMCLR | strobe Clears all horizontal motion registers |
| 002Cw | CXCLR | strobe Clears all collision registers |
TIA (read ghost)
These are the same registers as above but accessed with a ghost address to allow for different names.
| 0030r | CXM0P | XX...... Collisions D7=M0/P1, D6=M0/P0 |
| 0031r | CXM1P | XX...... Collisions D7=M1/P0, D6=M1/P1 |
| 0032r | CXP0FB | XX...... Collisions D7=P0/PF, D6=P0/BL |
| 0033r | CXP1FB | XX...... Collisions D7=P1/PF, D6=P1/BL |
| 0034r | CXM0FB | XX...... Collisions D7=M0/PF, D6=M0/BL |
| 0035r | CXM1FB | XX...... Collisions D7=M1/PF, D6=M1/BL |
| 0036r | CXBLPF | X....... Collisions D7=BL/PF |
| 0037r | CXPPMM | XX...... Collisions D7=P0/P1, D6=M0/M1 |
| 0038r | INPT0 | X....... Paddle input 0 |
| 0039r | INPT1 | X....... Paddle input 1 |
| 003Ar | INPT2 | X....... Paddle input 2 |
| 003Br | INPT3 | X....... Paddle input 3 |
| 003Cr | INPT4 | X....... Latched inputs (joystick buttons) |
| 003Dr | INPT5 | X....... Latched inputs (joystick buttons) |
PIA
The PIA (R.I.O.T.) is accessed if A12 is 0 and A7 is 1. If A9 is 0 then the 128 bytes of RAM are selected. If A9 is 1 then the PIA timer registers are selected.
The TIA REGS are selected if (address&1280 == 0280).
The TIA RAM is selected if (address&1280 == 0080).
The PIA chip uses the lower 7 address lines A0-A6. Thus the 007F mask below.
| 0280 | SWCHA | Port A Hand controllers |
| 0281 | SWACNT | Port A DDR |
| 0282 | SWCHB | Port B Console switches |
D7 : P1 difficulty (0=amateur, 1=pro) D6 : P0 difficulty (0=amateur, 1=pro) D5 : not used D4 : not used D3 : color or B/W (0=B/W, 1=color) D2 : not used D1 : game select (0=pressed) D0 : game reset (0=pressed)
| 0283 | SWBCNT | Port B DDR |
| 0284 | INTIM | Timer output (read only) |
| 0294 | TIM1T | Set 1 clock interval (write only) |
| 0295 | TIM8T | Set 8 clock interval (write only) |
| 0296 | TIM64T | Set 64 clock interval (write only) |
| 0297 | TIM1024T | Set 1024 clock interval (write only) |