Alternate VCS definitions

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File _defs.k65 provides alternate definitions of Atari 2600 registers. While use of this file is not required (standard VCS register names are predefined), after initial learning it can speed up prototyping by using shorter and lowercase names for all registers which are shorter and easier to type. This file also provides basic frame handling definitions and works well as quick reference to VCS register functions and bit patterns.

VCS register aliases

_defs.k65 provides following extra register alternative names.

TIA registers (Write)
Address Standard name Alternate name Description
00h VSYNC - Vertical sync set-clear
01h VBLANK - Vertical blank set-clear
02h WSYNC - Wait for leading edge of horizontal blank <strobe>
03h RSYNC - Reset horizontal sync counter <strobe>
04h NUSIZ0 ns0 Number-size player-missile 0
05h NUSIZ1 ns1 Number-size player-missile 1
06h COLUP0 cp0 Color Luminosity Player 0, Missile 0
07h COLUP1 cp1 Color Luminosity Player 1, Missile 1
08h COLUPF cpf Color Luminosity Playfield, Ball
09h COLUBK cbg Color Luminosity Background
0Ah CTRLPF ctpf Control Playfield and Ball size
0Bh REFP0 rep0 Reflect player 0
0Ch REFP1 rep1 Reflect player 1
0Dh PF0 pf0 Playfield Register 0 (LSB first) (only upper 4bit used)
0Eh PF1 pf1 Playfield Register 1 (MSB first) (8bit)
0Fh PF2 pf2 Playfield Register 2 (LSB first) (8bit)
10h RESP0 rp0 Reset player 0 <strobe>
11h RESP1 rp1 Reset player 1 <strobe>
12h RESM0 rm0 Reset missile 0 <strobe>
13h RESM1 rm1 Reset missile 1 <strobe>
14h RESBL rb Reset ball <strobe>
15h AUDC0 ac0 Audio Noise/Division Control, Channel 0
16h AUDC1 ac1 Audio Noise/Division Control, Channel 1
17h AUDF0 af0 Audio Frequency Divider, Channel 0
18h AUDF1 af1 Audio Frequency Divider, Channel 1
19h AUDV0 av0 Audio Volume, Channel 0
1Ah AUDV1 av1 Audio Volume, Channel 1
1Bh GRP0 gp0 Graphics (enable) player 0
1Ch GRP1 gp1 Graphics (enable) player 1
1Dh ENAM0 em0 Graphics (enable) missile 0
1Eh ENAM1 em1 Graphics (enable) missile 1
1Fh ENABL eb Graphics (enable) ball
20h HMP0 hp0 Horizontal motion player 0
21h HMP1 hp1 Horizontal motion player 1
22h HMM0 hm0 Horizontal motion missile 0
23h HMM1 hm1 Horizontal motion missile 1
24h HMBL hb Horizontal motion ball
25h VDELP0 vdp0 Vertical delay player 0 (Delay GRP0 until writing to GRP1)
26h VDELP1 vdp1 Vertical delay player 1 (Delay GRP1 until writing to GRP0)
27h VDELBL vdb Vertical delay ball (Delay ENABL until writing to GRP1)
28h RESMP0 rmp0 Reset missile 0 to player 0
29h RESMP1 rmp1 Reset missile 1 to player 1
2Ah HMOVE hmove Apply horizontal motion <strobe>
2Bh HMCLR hmclr Clear horizontal motion registers <strobe>
2Ch CXCLR (W) - Clear all collision latches <strobe>
TIA registers (Read)
Address Standard name Alternate name Description
30h CXM0P (R) - Collision Latch M0-P1, M0-P0 (Bit 7,6)
31h CXM1P (R) - Collision Latch M1-P0, M1-P1 (Bit 7,6)
32h CXP0FB (R) - Collision Latch P0-PF, P0-BL (Bit 7,6)
33h CXP1FB (R) - Collision Latch P1-PF, P1-BL (Bit 7,6)
34h CXM0FB (R) - Collision Latch M0-PF, M0-BL (Bit 7,6)
35h CXM1FB (R) - Collision Latch M1-PF, M1-BL (Bit 7,6)
36h CXBLPF (R) - Collision Latch BL-PF (Bit 7)
37h CXPPMM (R) - Collision Latch P0-P1, M0-M1 (Bit 7,6)
PIA registers
Address Standard name Alternate name Description
280h SWCHA swcha PIA Port A; input or output (R/W)
281h SWACNT - PIA Port A DDR Data Direction Register (R/W)
282h SWCHB swchb PIA Port B, Console Switches (R/W) (normally Read Only)
283h SWBCNT - PIA Port B DDR Data Direction Register (R/W)
284h INTIM - PIA Current Timer Value (Read only)
285h INSTAT - PIA Timer Status (Read only) (Undocumented)
294h TIM1T - PIA Set Timer & Select 1 clock interval (838ns/interval)
295h TIM8T - PIA Set Timer & Select 8 clock interval (6.7us/interval)
296h TIM64T - PIA Set Timer & Select 64 clock interval (53.6us/interval)
297h T1024T - PIA Set Timer & Select 1024 clock interval (858.2us/interval)

Special macros

_defs.k65 provides following extra inline macros.

Macro name Description
  init Clears entire zero page (including TIA regs), sets stack to RAM top, disables interrupts and decimal mode
 timwait Waits until PIA timer is zero (used in sync# macros)
 wsync Waits for horizontal blanking (simply WSYNC=a)
 sync1 Waits for timer and starts overscan (lower border) - you have approximately 45 scanlines (NTSC: 37) of overscan time after this.
 sync2 Waits for timer and pulses VSYNC and starts overscan (upper border) - you have approximately 36 scanlines (NTSC: 30) of overscan time after this.
 sync3 Waits for timer and visible screen portion - you have to generate approximately 228 scanlines (NTSC: 192) of visible picture now.

File source code

var zeropage = 0;
 
 
// Type        NTSC  PAL/SECAM
// V-Sync      3     3    scanlines
// V-Blank     37    45   scanlines (upper border)
// Picture     192   228  scanlines
// Overscan    30    36   scanlines (lower border)
// Frame Rate  60    50   Hz
// Frame Time  262   312  scanlines
 
// --- scanline numbers ---
// Type        NTSC		PAL/SECAM
// V-Sync      3		3    
// V-Blank     37		45   
// Picture     192		228  
// Overscan    30		36
 
 
 
 
 
inline init		{ i+ d-		s=x=0xFF	a=0 { zeropage,x=a x-- }!=	}
inline timwait	{ { a=INTIM }!= }
inline wsync	{ WSYNC=a }
 
// PAL:		0	45	275		312
// NTSC:	0	37	231		262
 
// PAL
inline sync1	{ timwait wsync VBLANK=a=2 TIM64T=a=40 }
inline sync2	{ timwait wsync VSYNC=a=2 wsync wsync a=0 wsync VSYNC=a TIM64T=a=54 }
inline sync3	{ timwait wsync VBLANK=a=0 T1024T=a=18 }
 
// NTSC
//inline sync1	{ timwait wsync VBLANK=a=2 TIM64T=a=33 }
//inline sync2	{ timwait wsync VSYNC=a=2 wsync wsync a=0 wsync VSYNC=a TIM64T=a=44 }
//inline sync3	{ timwait wsync VBLANK=a=0 TIM64T=a=231 }
 
 
 
 
var ns0=0x04,ns1;				// 00xx 0xxx   Number-Size player/missle 0/1
								//		 ^^^	- Player-Missile number & Player size (See table below)
								//		 000		  0  One copy              (X.........)
								//		 001		  1  Two copies - close    (X.X.......)
								//		 010		  2  Two copies - medium   (X...X.....)
								//		 011		  3  Three copies - close  (X.X.X.....)
								//		 100		  4  Two copies - wide     (X.......X.)
								//		 101		  5  Double sized player   (XX........)
								//		 110		  6  Three copies - medium (X...X...X.)
								//		 111		  7  Quad sized player     (XXXX......)
								//	 ^^			- Missile Size  (0..3 = 1,2,4,8 pixels width)
 
var cp0=0x06,cp1,cpf,cbg;		// xxxx xxx-   Color-Luminance Player 0/1, Playfield, Background
var ctpf=0x0A;					// --xx -xxx   Control Playfield, Ball, Collisions
								//		   ^	- Playfield Reflection     (0=Normal, 1=Mirror right half)
								//		  ^		- Playfield Color          (0=Normal, 1=Score Mode, only if Bit2=0)
								//		 ^		- Playfield/Ball Priority  (0=Normal, 1=Above Players/Missiles)
								//	 ^^			- Ball size                (0..3 = 1,2,4,8 pixels width)
 
var rep0=0x0B, rep1;			// ---- x---   Reflection Player 0/1
var pf0=0x0D, pf1, pf2;			// xxxx ----   Playfield Register Byte 0
								// xxxx xxxx   Playfield Register Byte 1
								// xxxx xxxx   Playfield Register Byte 2
var rp0=0x10,rp1,rm0,rm1,rb;	// ---- ----   Reset Player 0/1, Missile 0/1, Ball
 
var gp0=0x1B,gp1;				// xxxx xxxx   Graphics Register Player 0/1
var em0=0x1D,em1,eb;			// ---- --x-   Graphics Enable Missle 0/1, Ball
var hp0=0x20,hp1,hm0,hm1,hb;	// xxxx ----   Horizontal Motion Player 0/1, Missile 0/1, Ball
var vdp0=0x25,vdp1,vdb;			// ---- ---x   Vertical Delay Player 0/1, Ball
var rmp0=0x28,rmp1;				// ---- --x-   Reset Missle 0/1 to Player 0/1
var hmove=0x2A;					// ---- ----   Apply Horizontal Motion
var hmclr=0x2B;					// ---- ----   Clear Horizontal Move Registers
 
var gp0h=0x11B,gp1h;			// xxxx xxxx   Graphics Register Player 0/1
var rmp0h=0x128,rmp1h;			// ---- --x-   Reset Missle 0/1 to Player 0/1
var pf0h=0x10D, pf1h, pf2h;		// xxxx ----   Playfield Register Byte 0
var cp0h=0x106,cp1h,cpfh,cbgh;	// xxxx xxx-   Color-Luminance Player 0/1, Playfield, Background
var hp0h=0x120,hp1h,hm0h,hm1h,hbh;	// xxxx ----   Horizontal Motion Player 0/1, Missile 0/1, Ball
 
var ac0=0x15,ac1;				// ---- xxxx   Audio Control 0/1
var af0=0x17,af1;				// ---x xxxx   Audio Frequency 0/1
var av0=0x19,av1;				// ---- xxxx   Audio Volume 0/1
 
var inpt0=0x38;					// x--- ----   read pot port
var inpt1=0x39;					// x--- ----   read pot port
var inpt2=0x3A;					// x--- ----   read pot port
var inpt3=0x3B;					// x--- ----   read pot port
var inpt4=0x3C;					// x--- ----   read input / P0 Fire (0 active)
var inpt5=0x3D;					// x--- ----   read input / P1 Fire (0 active)
 
var swcha=0x280;				// xxxx xxxx   Port A
								//         ^	- P1 Up		(0 active)
								//        ^		- P1 Down	(0 active)
								//       ^		- P1 Left	(0 active)
								//      ^		- P1 Right	(0 active)
								//    ^			- P0 Up		(0 active)
								//   ^			- P0 Down	(0 active)
								//  ^			- P0 Left	(0 active)
								// ^			- P0 Right	(0 active)
 
var swchb=0x282;				// xx-- x-xx   Port B
								//         ^	- Reset Button          (0=Pressed)
								//		  ^		- Select Button         (0=Pressed)
								//      ^		- Color Switch          (0=B/W, 1=Color) (Always 0 for SECAM)
								//  ^			- P0 Difficulty Switch  (0=Beginner (B), 1=Advanced (A))
								// ^			- P1 Difficulty Switch  (0=Beginner (B), 1=Advanced (A))
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