Programming the 2600 (with some 7800 info)From: Michael Current (aa700@cleveland.Freenet.Edu)
Date: 12/08/92-11:03:17 AM Z
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From: aa700@cleveland.Freenet.Edu (Michael Current) Subject: Programming the 2600 (with some 7800 info) Date: Tue Dec 8 11:03:17 1992 Specifications for the Atari 2600/7800 2600 7800 CPU: 6507 6502C (custom, NOT 65C02) RAM: 128 Bytes, in VLSI 4K, high speed ROM: 6K max 52K max Cpu Clock: 1.19 MHz 1.79 MHz Graphics Clock: 3.58 MHz 7.16 MHz Slot Config: Rom access only Most CPU lines + video/audio CPU Avail: less than 50% over 90% Notes: 1. ROM specs are based on a non-bank select scheme. 2. Graphics Clock is the master clock used to drive the video chips. Programming the 2600 in a nutshell. The Atari 2600 consists of 3 important ICs: the CPU (6507), the Television Interface Adapter (TIA or Stella), and the RIOT (6532). The 7800 has a CPU (6502C or Sally) instead of the 6507 and a GCC1702 (Maria) chip in addition to the Stella chip. The CPU: The 6507 CPU is a 6502 with 2 important exceptions: it only has external address lines for 8K of memory and there are NO interrupt lines connected. This is not as limiting as it seems if you examine some of the games for the machine. The Stella chip: This chip makes all the video displays and sounds for the 2600 VCS. It also has 6 registers which are used as A/D converters and for the trigger buttons on the joysticks. The chip also controls the RDY line of the CPU to initiate horizontal syncronization control. The chip is NOT a DMA chip. The CPU must write each line of data into the chip registers AS it draws the screen. This accounts for the low CPU availability. The Chip is addresed through 44 write only registers, and 13 read only registers mapped to the low end of page 0. For those familiar with the Atari 800, this chip is about 1/2 of a TIA/Pokey in all respects. But, there is no ANTIC chip to drive it; the CPU must do all the work that the ANTIC does in the 800. The RIOT This chip reads all the console switches (excluding power), the joysticks, and other controllers. It also contains the only RAM in the system and a general purpose timer. The RAM is mapped to the high end of both page 0 and page 1. This means that it acts as both page 0 fast access memory and the 6502 stack. The timer and I/O ports are mapped to Page 2 and 3. In order to produce a video display, a program must do the following: 1. Start the vertical blanking interval 2. Start the vertical sync interval immediately there is time for about 80 instructions after this 3. End vertical sync the game computations must be done now as there won't be time later 4. End vertical blanking 5. Set up each line of the video display as it is drawn there is time for about 6 instructions to the video chip before the current line starts being displayed. Atari recommends changing the display every other line to gain processing time. 6. Loop back to step 1 The Cartridge: A standard cartridge contains the equivalent of a 2716 or 2732/2532 with one notable exception: the chip select line is active high, not low. The high order address line of the 6507 (A12) is used as the chip enable. There was at least one company that used EPROMs with a 74LS04 inverter to compensate for this. The Pinouts: Note: numbers indicate left to right numbering Top Row Bottom Row Slot 2716 CPU 2716 CPU 1 13 D3 1 A7 2 14 D4 2 A6 3 15 D5 3 A5 4 16 D6 4 A4 5 17 D7 5 A3 6 * A12 6 A2 7 19 A10 7 A1 8 NC A11 8 A0 9 22 A9 9 D0 10 23 A8 10 D1 11 24 +5V 11 D2 12 12 Shield Ground NC Ground * to inverter and back to 18 for chip select Major differences between 2600 and 7800 mode: 2600 mode is default in the 7800. If it finds 128 bytes at the high end of memory to match its encryption scheme, it will enable 7800 mode. There is a small ROM inside the unit which displays the Atari pattern on screen as it does this. The 7800 mode is DMA driven, so the processor is free most of the time to do other things, as the graphics chip runs 4 times faster than the CPU. The 7800 cartridge slot includes 8 more lines: A13, A14, A15, R/W, phase 2 clock, audio, video, and HALT (unique to Atari 6502). The 2600 video has foreground/background, 2 player/missles, and one ball. The 7800 can display as many objects as the DMA can read in one line. The sound is exactly the same as it still uses the Stella chip (except Ballblazer which has its own sound chip in the cartridge). --- graphics.txt --- Wsync Wait for sync This address halts microprocessor by clearing RDY latch to zero. RDY is set true again by the leading edge of horizontal blank. Data bits not used. --- Rsync Reset Sync This address resets the horizontal sync counter to define the begining of horizontal blank time, and is used in chip testing. Data bits not used. --- Vsync This address controls vertical sync time by writing D1 into the Vsync latch. D1 - 1: start vertical sync 0: stop vertical sync --- Vblank This address controls vertical blank and the latches and dumping transistors on the input ports by writing into bits D7,D6, and D1 of the Vblank register. D1 - 1: start vertical blank 0: stop vertical blank D6 - 1: enable I4 and I5 latches 0: disable latches - also resets latches to logic true D7 - 1: Dump I0,I1,I2,I3 ports to ground 0: Remove dump path to ground --- Pf0, Pf1, Pf2 These addresses are used to write into the playfield registers. horizontal scan line map (160 clocks, each bit =4 clocks) Ctrlpf bit 0 bits 4-7 7-0 0-7 | 4-7 7-0 0-7 register Pf0 Pf1 Pf2 Pf0 Pf1 Pf2 0 bits 4-7 7-0 0-7 | 7-0 0-7 7-4 register Pf0 Pf1 Pf2 Pf2 Pf1 Pf0 1 --- Ctrlpf This address is used to write into the playfield control register. if bit is 1 then: D0 - (REF) reflect playfield, see above D1 - (SCORE) left half of playfield gets color of player 0 right half gets color of player 1 D2 - (PFP) playfield gets priority over players so they move behind playfield D5,D4 - Ball Size if 00, 1 clock wide if 01, 2 clocks wide if 10, 4 clocks wide if 11, 8 clocks wide --- Nusiz0, Nusiz1 These addresses control the number and size of players and missles. D5,D4 - Missle Size see Ball Size above D2,D1,D0 - Player number/size if 000, X one copy if 001, X X two copies, close if 010, X X two copies, medium if 011, X X X three copies, close if 100, X X Two copies, far if 101, XX one copy, double width if 110, X X X 3 copies, medium if 111, XXXX one copy, quad width --- Resp0, Resp1, Resm0, Resm1, Resbl These addresses are used to reset players, missles and the ball. The object will begin its serial graphics at that time of a horizontal line at which the reset address occurs. Data bits not used. --- Resmp0, Resmp1 These addresses are used to reset the horizontal location of a missle to the center of its corresponding player. As long as this control bit is true (1), the misslw will remain locked to the center of its player and the mis sle graphics will be disabled. When a zero is written into this location, the missle is enabled, and can be moved independently from the player. D1 - 0: allow missle to move 1: lock missle to player --- Hmove This address causes the horizontal motion register values to be acted upon during the horizontal blank time in which it occurs. It must occur at the beginning of horizontal blanking in order to allow time for generation of extra clock pulses into the horizontal position counters. If motion is desired, this command must immediately follow a Wsync command in the program. Data bits not used. --- Hmclr This address clears all horizontal motion registers to zero (no motion). Data bits not used. --- Hmp0, Hmp1, Hmm0, Hmm1, Hmbl These addresses write data (horizontal motion values) into the horizontal motion registers. These registers cause horizontal motion only when commanded to do so by the horizontal movement command Hmove. The motion values use the upper 4 bits of the byte. They are signed numbers with a +7 to -8 range. The positive numbers indicate left movement, the negative indicate right. Warning: These registers should not be modified during the 24 computer cycles following an Hmove command. Unpredictable motion values may result. --- Enam0, Enam1, Enabl These addresses write into the single bit missle or ball graphics registers. D1 - 0: disables object 1: enables object --- Grp0, Grp1 These addresses write data into the player graphics registers horizontal scan line map (each bit =1 clock) bits 7-0 if Refp0 (Refp1) is 0 bits 0-7 if Refp0 (Refp1) is 1 (reflected) --- Refp0, Refp1 These addresses write data into the the single bit player reflect registers. see above. D3 - 0: normal 1: reflected --- Vdelp0, Vdelp1, Vdelbl These addresses write data into the single bit vertical delay registers, to delay players or the ball by one vertical line. D0 - 0: no delay 1: delayed --- Cxclr This address clears all collision latches to zero (no collision) Data bits not used. --- Colupb, Colup1, Colupf, Colubk These addresses write data into the player, playfield, and background color-luminance registers. D3, D2, D1 - Luminance values 000 is dark, 111 is bright. D7,D6,D5,D4 - Colors 0000 Grey 0001 Gold 0010 Orange 0011 Red orange 0100 Pink 0101 Purple 0110 Blue purple 0111 Blue 1000 Blue 1001 Light blue 1010 Turquoise 1011 Green blue 1100 Green 1101 Yellow green 1110 Orange green 1111 Light orange --- Audf0, Audf1 These addresses write data into the audio frequency divider registers. D4,D3,D2,D1,D0 - 00000 30KHz divided by 1 00001 " " 2 ..... 11111 " " 32 --- Audc0, Audc1 These addresses write data into the audio control registers which control the noise content and additional division of the audio output. bits value noise type division D3, D2, D1, D0 - 0000 set to 1 0001 4 bit poly 0010 /15 into 4 bit poly 0011 5 bit poly into 4 bit poly 0100 divide by 2 0101 divide by 2 0110 divide by 31 0111 5 bit poly into /2 1000 9 bit poly 1001 5 bit poly 1010 divide by 31 1011 set last 4 bits to 1 1100 divide by 6 1101 divide by 6 1110 divide by 93 1111 5 bit poly divided by 6 --- Audv0, Audv1 These addresses write data into the audio volume registers which set the pull down impedance driving the audio output pads. D3, D2, D1, D0 - 0000 no output .... 1111 loudest output --- End --- stella.txt --- Atari 2600 Stella Memory Map Write Address Registers Addr Assy Name Bits Used Function 00 Vsync 0000 00x0 Vertical Sync Set-Clear 01 Vblank xx00 00x0 Vertical Blank Set-Clear 02 Wsync ---- ---- Wait for Horizontal Blank 03 Rsync ---- ---- Reset Horizontal Sync Counter 04 Nusiz0 00xx 0xxx Number-Size player/missle 0 05 Nusiz1 00xx 0xxx Number-Size player/missle 1 06 Colup0 xxxx xxx0 Color-Luminance Player 0 07 Colup1 xxxx xxx0 Color-Luminance Player 1 08 Colupf xxxx xxx0 Color-Luminance Playfield 09 Colubk xxxx xxx0 Color-Luminance Background 0A Ctrlpf 00xx 0xxx Control Playfield, Ball, Collisions 0B Refp0 0000 x000 Reflection Player 0 0C Refp1 0000 x000 Reflection Player 1 0D Pf0 xxxx 0000 Playfield Register Byte 0 0E Pf1 xxxx xxxx Playfield Register Byte 1 0F Pf2 xxxx xxxx Playfield Register Byte 2 10 Resp0 ---- ---- Reset Player 0 11 Resp1 ---- ---- Reset Player 1 12 Resm0 ---- ---- Reset Missle 0 13 Resm1 ---- ---- Reset Missle 1 14 Resbl ---- ---- Reset Ball 15 Audc0 0000 xxxx Audio Control 0 16 Audc1 0000 xxxx Audio Control 1 17 Audf0 000x xxxx Audio Frequency 0 18 Audf1 000x xxxx Audio Frequency 1 19 Audv0 0000 xxxx Audio Volume 0 1A Audv1 0000 xxxx Audio Volume 1 1B Grp0 xxxx xxxx Graphics Register Player 0 1C Grp1 xxxx xxxx Graphics Register Player 1 1D Enam0 0000 00x0 Graphics Enable Missle 0 1E Enam1 0000 00x0 Graphics Enable Missle 1 1F Enabl 0000 00x0 Graphics Enable Ball 20 Hmp0 xxxx 0000 Horizontal Motion Player 0 21 Hmp1 xxxx 0000 Horizontal Motion Player 1 22 Hmm0 xxxx 0000 Horizontal Motion Missle 0 23 Hmm1 xxxx 0000 Horizontal Motion Missle 1 24 Hmbl xxxx 0000 Horizontal Motion Ball 25 Vdelp0 0000 000x Vertical Delay Player 0 26 Vdelp1 0000 000x Vertical Delay Player 1 27 Vdelbl 0000 000x Vertical Delay Ball 28 Resmp0 0000 00x0 Reset Missle 0 to Player 0 29 Resmp1 0000 00x0 Reset Missle 1 to Player 1 2A Hmove ---- ---- Apply Horizontal Motion 2B Hmclr ---- ---- Clear Horizontal Move Registers 2C Cxclr ---- ---- Clear Collision Latches Read Address Registers bit 6 bit 7 0 Cxm0p xx00 0000 Read Collision M0-P1 M0-P0 1 Cxm1p xx00 0000 M1-P0 M1-P1 2 Cxp0fb xx00 0000 P0-PF P0-BL 3 Cxp1fb xx00 0000 P1-PF P1-BL 4 Cxm0fb xx00 0000 M0-PF M0-BL 5 Cxm1fb xx00 0000 M1-PF M1-BL 6 Cxblpf x000 0000 BL-PF ----- 7 Cxppmm xx00 0000 P0-P1 M0-M1 8 Inpt0 x000 0000 Read Pot Port 0 9 Inpt1 x000 0000 Read Pot Port 1 A Inpt2 x000 0000 Read Pot Port 2 B Inpt3 x000 0000 Read Pot Port 3 C Inpt4 x000 0000 Read Input (Trigger) 0 D Inpt5 x000 0000 Read Input (Trigger) 1 Atari 2600 RIOT Memory Map 80-FF Ram also at 180-1FF 280 Swcha Port A data register (joysticks...) 281 Swacnt Port A data direction register (DDR) 282 Swchb Port B data (console switches) 283 Swbcnt Port B DDR 284 Intim Timer output 294 Tim1t set 1 clock interval 295 Tim8t set 8 clock interval 296 Tim64t set 64 clock interval 297 T1024t set 1024 clock interval these are also at 380-397 Atari 2600 ROM Memory Map E000-FFFF Rom also 1000-1FFF 3000-3FFF .... --- colrdemo.asm --- ; Color Demo ; Taken from the Magicard Manual ; shows almost all the colors on the left side ; of the screen and cycles slowly on the right ; Start LDA $81 ; get contents of memory STA $0F ; save into a pattern control register LDA #$03 STA $0A ; set background control register LDA #$55 STA $07 ; set right side color LDY #$00 DEY STA $02 ; wait for horizontal sync STA $01 ; start vertical blanking STA $00 ; start vertical retrace LDA #$2A STA $0295 ; set timer for appropriate length Loop1 LDY $0284 BNE Loop1 ; waste time STY $02 ; wait for horizontal sync STY $00 ; end vertical retrace period LDA #$24 STA $0296 ; set timer for next wait LDA $0282 AND #$01 ; check for reset switch BNE NReset BRK ; only interrupt available - must have vector set NReset INC $80 ; increment right side color cycle counter BNE Loop2 LDA #$E0 STA $80 ; reset counter INC $81 LDA $81 ; increment right side color STA $06 ; store it in color register Loop2 LDY $0284 BNE Loop2 ; waste time STY $02 ; wait for horizontal sync STY $01 ; end vertical blanking LDX #$E4 ; number of line to draw on screen Loop3 STY $02 ; wait for horizontal sync STX $0E ; change a background pattern with each line STX $07 ; change right side color with each line DEX BNE loop3 JMP Start ; do next screen (every 1/60th second) .END --- bilboard.asm --- ; Billboard Demo ; displays sonething close to, but not quite like ; the colored billboard used in "Close Encounters..." ; just a small demo to see what could be done ; Start LDX #$FF TXS JSR Sub0 LDA #$06 STA $09 LDA #$02 STA $0A LDA #$35 STA $B1 STA $B4 LDA $1B STA $B2 STA $B3 LDA #$00 STA $B6 LDA #$AA STA $B5 Main JSR Sub1 LDA #$50 STA $06 LDA #$80 STA $07 LDA #$08 STA $19 JSR Sub2 LDA $0282 AND #$02 BEQ Start JSR Sub3 LDX #$10 Loop1 NOP STY $02 DEX BNE Loop1 LDY #$06 LDX #$04 Loop2 STY #$02 LDA $B1 STA $0D LDA $B2 STA $0E LDA $B3 STA $0F NOP NOP NOP NOP NOP NOP NOP LDA $B4 STA $0D LDA $B5 STA $0E LDA $B6 STA $0F DEX BNE Loop2 LDA #$06 STA $06 STA $07 LDX #$A6 Loop3 NOP STY $02 DEX BNE Loop3 JMP Main Sub0 CLD SEI LDX #$00 STX $0281 STX $0283 LDY #$04 Loc0 STX $00,Y INY CPY #$20 BNE Loc0 STX $2B RTS Sub1 LDY #$FF STY $02 STY $01 STY $00 LDA #$2A STA $0295 LDA $0282 AND #$01 BNE Loc1 BRK Loc1 RTS Sub2 LDY $0284 BNE Sub2 STY $02 STY $00 LDA #$19 STA $0296 RTS Sub3 LDY $0284 BNE Sub3 STY $02 STY $01 STY $2A RTS .END -- Michael Current, Cleveland Free-Net 8-bit Atari SIGOp Carleton College, Northfield, MN, USA / UUCP: ...!umn-cs!ccnfld!currentm Internet: email@example.com / Cleveland Free-Net: aa700
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