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Altirra Hardware

Reference Manual2023-05-29 Edition

Avery Lee

Altirra Hardware Reference ManualCreated by Avery Lee

Table of Contents

1.1 . Introduction ............................................................................................................................................ 10

1.2 . What's new in this edition ....................................................................................................................... 11

1.3 . Conventions in this manual .................................................................................................................... 18

1.4 . Concepts ................................................................................................................................................ 20

2 . System Architecture ...................................................................................................................................... 24

2.1 . Basic architecture .................................................................................................................................. 25

2.2 . Clocks .................................................................................................................................................... 28

2.3 . Memory system ..................................................................................................................................... 29

2.4 . System Reset button ............................................................................................................................. 30

2.5 . Peripheral Interface Adapter (PIA) ......................................................................................................... 31

2.6 . Bank switching ....................................................................................................................................... 33

2.7 . Extended memory .................................................................................................................................. 34

2.8 . Miscellaneous connections .................................................................................................................... 36

2.9 . Examples ............................................................................................................................................... 36

2.10 . Further reading .................................................................................................................................... 37

3 . CPU .............................................................................................................................................................. 38

3.1 . Flags ...................................................................................................................................................... 39

3.2 . Decimal mode ........................................................................................................................................ 40

3.3 . Cycle timing ........................................................................................................................................... 41

3.4 . Interrupts ................................................................................................................................................ 43

3.5 . Undocumented instructions ................................................................................................................... 46

3.6 . 65C02 compatibility ............................................................................................................................... 49

3.7 . 65C816 compatibility ............................................................................................................................. 51

3.8 . 65C816 new features ............................................................................................................................. 52

3.9 . Examples ............................................................................................................................................... 54

3.10 . Further reading .................................................................................................................................... 55

4 . ANTIC ........................................................................................................................................................... 56

4.1 . Basic operation ...................................................................................................................................... 57

4.2 . Display timing ........................................................................................................................................ 58

4.3 . Playfield ................................................................................................................................................. 59

4.4 . Character modes ................................................................................................................................... 60

4.5 . Mapped (bitmap) modes ........................................................................................................................ 62

4.6 . Display list .............................................................................................................................................. 63

4.7 . Scrolling ................................................................................................................................................. 66

4.8 . Non-maskable interrupts ........................................................................................................................ 71

4.9 . WSYNC ................................................................................................................................................. 74

4.10 . VCOUNT .............................................................................................................................................. 75

4.11 . Playfield DMA ....................................................................................................................................... 75

4.12 . Abnormal playfield DMA ....................................................................................................................... 77

4.13 . Player/missile DMA .............................................................................................................................. 82

4.14 . Scan line timing ................................................................................................................................... 82

4.15 . Cycle counting example ....................................................................................................................... 93

4.16 . Examples ............................................................................................................................................. 95

4.17 . Further reading .................................................................................................................................... 96

5 . POKEY ......................................................................................................................................................... 97

5.1 . Addressing ............................................................................................................................................. 98

5.2 . Initialization ............................................................................................................................................ 98

5.3 . Sound generation .................................................................................................................................. 99

5.4 . Clock generation .................................................................................................................................. 106

5.5 . Noise generators ................................................................................................................................. 106

- 2 Altirra Hardware Reference ManualCreated by Avery Lee

5.6 . Serial port ............................................................................................................................................ 107

5.7 . Interrupts .............................................................................................................................................. 116

5.8 . Keyboard scan ..................................................................................................................................... 117

5.9 . Paddle scan ......................................................................................................................................... 121

5.10 . Examples ........................................................................................................................................... 123

5.11 . Further reading ................................................................................................................................... 123

6 . CTIA/GTIA .................................................................................................................................................. 124

6.1 . System role .......................................................................................................................................... 125

6.2 . Display generation ............................................................................................................................... 126

6.3 . Color encoding ..................................................................................................................................... 126

6.4 . Artifacting ............................................................................................................................................. 129

6.5 . Player/missile graphics ........................................................................................................................ 131

6.6 . Collision detection ................................................................................................................................ 135

6.7 . Priority control ...................................................................................................................................... 136

6.8 . High resolution mode (ANTIC modes 2, 3, and F) ............................................................................... 138

6.9 . GTIA special modes ............................................................................................................................. 139

6.10 . Cycle timing ....................................................................................................................................... 141

6.11 . General purpose I/O ........................................................................................................................... 143

6.12 . Further reading .................................................................................................................................. 143

7 . Accessories ................................................................................................................................................. 144

7.1 . Joystick ................................................................................................................................................ 145

7.2 . Paddle .................................................................................................................................................. 145

7.3 . Mouse .................................................................................................................................................. 146

7.4 . Light Pen/Gun ...................................................................................................................................... 147

7.5 . CX-75 Light Pen .................................................................................................................................. 148

7.6 . Stack Lightpen ..................................................................................................................................... 150

7.7 . CX-85 Numerical Keypad .................................................................................................................... 150

7.8 . CX-20 Driving Controller ...................................................................................................................... 151

7.9 . CX-21/23/50 Keyboard Controller ........................................................................................................ 151

7.10 . XEP80 Interface Module .................................................................................................................... 152

7.11 . Corvus Disk System ........................................................................................................................... 166

7.12 . ComputerEyes Video Acquisition System .......................................................................................... 167

8 . Cartridges ................................................................................................................................................... 170

8.1 . Cartridge port ....................................................................................................................................... 171

8.2 . Atarimax flash cartridges ...................................................................................................................... 172

8.3 . Atarimax MyIDE-II ................................................................................................................................ 173

8.4 . SIC! ...................................................................................................................................................... 175

8.5 . SIDE 1 / SIDE 2 ................................................................................................................................... 176

8.6 . SIDE 3 ................................................................................................................................................. 179

8.7 . Corina .................................................................................................................................................. 192

8.8 . R-Time 8 .............................................................................................................................................. 192

8.9 . Veronica ............................................................................................................................................... 193

9 . Serial I/O (SIO) Bus .................................................................................................................................... 198

9.1 . Basic SIO protocol ............................................................................................................................... 199

9.2 . Polling .................................................................................................................................................. 203

9.3 . 820 40 Column Printer ......................................................................................................................... 206

9.4 . 820 hardware ....................................................................................................................................... 206

9.5 . 850 Interface Module ........................................................................................................................... 208

9.6 . 1030 Modem ........................................................................................................................................ 211

9.7 . SX212 Modem ..................................................................................................................................... 213

9.8 . R-Verter ............................................................................................................................................... 215

9.9 . 410/1010 Program Recorder ............................................................................................................... 215

9.10 . MidiMate ............................................................................................................................................ 216

9.11 . Pocket Modem ................................................................................................................................... 216

- 3 Altirra Hardware Reference ManualCreated by Avery Lee

10 . Disk drives ................................................................................................................................................ 218

10.1 . Introduction ........................................................................................................................................ 219

10.2 . Basic protocol .................................................................................................................................... 226

10.3 . Extended protocols ............................................................................................................................ 228

10.4 . Commands ........................................................................................................................................ 231

10.5 . Timing ................................................................................................................................................ 232

10.6 . Anomalies .......................................................................................................................................... 238

10.7 . 6532 RIOT ......................................................................................................................................... 241

10.8 . 177X/179X/279X FDC ....................................................................................................................... 242

10.9 . 810 disk drive ..................................................................................................................................... 244

10.10 . 810 hardware ................................................................................................................................... 247

10.11 . Happy 810 ........................................................................................................................................ 250

10.12 . 810 Turbo ......................................................................................................................................... 252

10.13 . 815 disk drive ................................................................................................................................... 254

10.14 . 815 hardware ................................................................................................................................... 256

10.15 . 1050 disk drive ................................................................................................................................. 259

10.16 . 1050 hardware ................................................................................................................................. 263

10.17 . 1450XLD disk drive .......................................................................................................................... 265

10.18 . 1450XLD disk hardware ................................................................................................................... 267

10.19 . US Doubler ...................................................................................................................................... 269

10.20 . Happy 1050 ..................................................................................................................................... 270

10.21 . I.S. Plate .......................................................................................................................................... 276

10.22 . XF551 disk drive .............................................................................................................................. 277

10.23 . XF551 hardware .............................................................................................................................. 280

10.24 . Indus GT disk drive .......................................................................................................................... 281

10.25 . Indus GT hardware .......................................................................................................................... 284

10.26 . ATR8000 hardware .......................................................................................................................... 286

10.27 . Percom RFD .................................................................................................................................... 289

10.28 . Percom AT88 ................................................................................................................................... 291

10.29 . Percom AT88-SPD/S1PD ................................................................................................................ 293

10.30 . Amdek AMDC-I/II ............................................................................................................................. 296

11 . Parallel Bus Interface ................................................................................................................................ 300

11.1 . Introduction ........................................................................................................................................ 301

11.2 . Common memory map ....................................................................................................................... 301

11.3 . ICD Multi I/O (MIO) ............................................................................................................................ 302

11.4 . CSS Black Box ................................................................................................................................... 305

11.5 . Atari 1090 80 Column Video Card ...................................................................................................... 308

11.6 . Atari 1400XL/1450XLD ....................................................................................................................... 310

12 . Internal devices ......................................................................................................................................... 312

12.1 . Introduction ........................................................................................................................................ 313

12.2 . Covox ................................................................................................................................................. 313

12.3 . Ultimate1MB ...................................................................................................................................... 313

12.4 . VideoBoard XE .................................................................................................................................. 321

12.5 . APE Warp+ OS 32-in-1 ...................................................................................................................... 336

12.6 . Bit-3 Full-View 80 ............................................................................................................................... 337

13 . 5200 SuperSystem ................................................................................................................................... 340

13.1 . Introduction ........................................................................................................................................ 341

13.2 . Differences from the 8-bit computer line ............................................................................................ 341

13.3 . Controller ........................................................................................................................................... 342

13.4 . 5200 Memory map ............................................................................................................................. 344

14 . Reference ................................................................................................................................................. 345

14.1 . Memory map ...................................................................................................................................... 346

14.2 . Register list ........................................................................................................................................ 347

14.3 . GTIA registers .................................................................................................................................... 348

- 4 Altirra Hardware Reference ManualCreated by Avery Lee

14.4 . POKEY registers ................................................................................................................................ 368

14.5 . PIA registers ...................................................................................................................................... 384

14.6 . ANTIC registers ................................................................................................................................. 388

14.7 . Register listing ................................................................................................................................... 400

15 . Bibliography .............................................................................................................................................. 403

A . Polynomial Counters ................................................................................................................................... 406

B . Physical Disk Format .................................................................................................................................. 411

B.1 . Raw geometry ..................................................................................................................................... 412

B.2 . Bit encoding ......................................................................................................................................... 412

B.3 . Address field ........................................................................................................................................ 413

B.4 . Data field ............................................................................................................................................. 414

B.5 . CRC algorithm ..................................................................................................................................... 414

C . Physical Tape Format ................................................................................................................................. 416

C.1 . Signal encoding ................................................................................................................................... 417

C.2 . Framing ............................................................................................................................................... 417

C.3 . FSK demodulation ............................................................................................................................... 417

C.4 . Zero crossing detection ....................................................................................................................... 417

C.5 . Peak detection .................................................................................................................................... 417

C.6 . DFT detection ...................................................................................................................................... 418

C.7 . Quadrature demodulation .................................................................................................................... 420

C.8 . Asynchronous serial decoding ............................................................................................................ 421

D . Analog Video Model ................................................................................................................................... 422

D.1 . Introduction ......................................................................................................................................... 423

D.2 . NTSC color encoding .......................................................................................................................... 423

D.3 . NTSC artifacting .................................................................................................................................. 431

D.4 . PAL color encoding ............................................................................................................................. 435

D.5 . PAL artifacting ..................................................................................................................................... 437

E . Analog Audio Model .................................................................................................................................... 440

E.1 . Introduction .......................................................................................................................................... 441

E.2 . POKEY output ..................................................................................................................................... 441

E.3 . First amplifier stage ............................................................................................................................. 442

E.4 . External signal sum point .................................................................................................................... 443

E.5 . Second amplifier stage ........................................................................................................................ 443

E.6 . Final output .......................................................................................................................................... 445

F . Quick Reference ......................................................................................................................................... 446

F.1 . CPU opcode table ................................................................................................................................ 447

- 5 Altirra Hardware Reference ManualCreated by Avery Lee

Index of Tables

Table 1: Some extended memory configurations..................................................................................................35

Table 2: NMOS 6502 opcode table.......................................................................................................................46

Table 3: 65C02 opcode table................................................................................................................................50

Table 4: 65C816 opcode table..............................................................................................................................51

Table 5: Typical power-up values for ANTIC registers...........................................................................................58

Table 6: ANTIC display timing...............................................................................................................................58

Table 7: DMA and shift clock rates by mode.........................................................................................................78

Table 8: Distortion modes...................................................................................................................................101

Table 9: POKEY clock frequencies.....................................................................................................................106

Table 10: Serial port timing modes......................................................................................................................110

Table 11: Key codes (scan matrix layout)............................................................................................................118

Table 12: Key codes (130XE keyboard layout)...................................................................................................118

Table 13: GTIA Register Map..............................................................................................................................125

Table 14: PAL GTIA color encodings...................................................................................................................128

Table 15: Results of various size changes in the middle of a player image........................................................134

Table 16: Priority logic outputs for unusual priority modes..................................................................................137

Table 17: ANx bus encodings..............................................................................................................................141

Table 18: Timing for mid-screen writes to GTIA registers....................................................................................142

Table 19: CX-85 keypad to PORTA bit pattern mapping.....................................................................................150

Table 20: Keyboard Controller key matrix...........................................................................................................151

Table 21: Character bit to block graphics mapping.............................................................................................155

Table 22: XEP80 Timing Register Values............................................................................................................165

Table 23: Corvus Interface modes......................................................................................................................167

Table 24: ComputerEyes controller port usage...................................................................................................168

Table 25: SIDE 1/2 register map.........................................................................................................................177

Table 26: SIDE 3 registers..................................................................................................................................181

Table 27: SIDE 3 registers changed by push button reset..................................................................................182

Table 28: SIO device IDs....................................................................................................................................200

Table 29: Peripheral Handler Relocation Record Types......................................................................................205

Table 30: 820 memory map................................................................................................................................207

Table 31: 820 RIOT port assignments.................................................................................................................207

Table 32: 1030 Modem hardware commands.....................................................................................................212

Table 33: SX212 supported commands..............................................................................................................214

Table 34: Disk drive status frame........................................................................................................................227

Table 35: Disk drive transfer rates......................................................................................................................229

Table 36: PERCOM Block Contents...................................................................................................................229

Table 37: Detected Percom blocks for various disk drives and formats..............................................................231

Table 38: Disk drive transmit timings by firmware...............................................................................................233

Table 39: Disk drive step rate timings.................................................................................................................234

Table 40: Disk format strategies by drive type....................................................................................................235

Table 41: Track sector layouts by drive type and format.....................................................................................238

Table 42: FDC status codes for various read sector conditions..........................................................................238

Table 43: Disk drive behavior on Read Sector command with drive door/latch open and no disk inserted.........239

Table 44: Ideal 810 sector read timing................................................................................................................241

Table 45: Step rates for various FDC models.....................................................................................................243

Table 46: Head load delays for various FDC models..........................................................................................243

Table 47: 810 drive firmware revisions................................................................................................................246

Table 48: 810 memory map................................................................................................................................248

Table 49: 810 RIOT I/O port assignments...........................................................................................................249

Table 50: Happy 810 memory map.....................................................................................................................250

Table 51: Happy 810 rev.7 drive mode bits.........................................................................................................252

- 6 Altirra Hardware Reference ManualCreated by Avery Lee

Table 52: 810 Turbo memory map......................................................................................................................253

Table 53: 815 memory map................................................................................................................................257

Table 54: 815 RIOT I/O port assignments...........................................................................................................258

Table 55: 1050 returned ROM signatures...........................................................................................................260

Table 56: 1050 memory map..............................................................................................................................264

Table 57: 1050 RIOT I/O port assignments.........................................................................................................265

Table 58: 1450XLD non-TONG controller I/O map.............................................................................................268

Table 59: 1450XLD TONG controller I/O map.....................................................................................................269

Table 60: Happy 1050 Memory Map...................................................................................................................271

Table 61: Happy 1050 drive mode bits................................................................................................................275

Table 62: XF551 drive status flags......................................................................................................................277

Table 63: XF551 PERCOM configuration block values.......................................................................................278

Table 64: XF551 firmware revisions....................................................................................................................279

Table 65: XF551 8040 I/O port connections........................................................................................................281

Table 66: Indus GT stock firmware revisions......................................................................................................282

Table 67: Commonly used Indus GT uploadable code fragments.......................................................................283

Table 68: Indus GT memory map........................................................................................................................284

Table 69: Indus GT status 1 port signals.............................................................................................................285

Table 70: Indus GT status 2 port signals.............................................................................................................285

Table 71: ATR8000 input port assignments.........................................................................................................287

Table 72: ATR8000 drive control port layout (OUT 30-3FH)................................................................................288

Table 73: ATR8000 SIO status port layout (IN 70-7FH)......................................................................................289

Table 74: ATR8000 printer status port layout (IN 20-2FH)..................................................................................289

Table 75: Percom RFD firmware revisions..........................................................................................................290

Table 76: Percom RFD-40S1 memory map........................................................................................................290

Table 77: Percom AT88 firmware revisions.........................................................................................................292

Table 78: Percom AT88-S1 memory map...........................................................................................................292

Table 79: Percom AT88-S1 PIA connections.......................................................................................................293

Table 80: Percom AT88-SPD/S1PD firmware revisions......................................................................................294

Table 81: Percom AT88-SPD/S1PD memory map..............................................................................................294

Table 82: Percom AT88-SPD/S1PD PIA connections.........................................................................................295

Table 83: Amdek AMDC-I/II memory map...........................................................................................................298

Table 84: MIO memory map................................................................................................................................302

Table 85: Black Box memory map......................................................................................................................305

Table 86: 80CVC hardware registers..................................................................................................................309

Table 87: VBXE extended display list (XDL) entry format...................................................................................322

Table 88: VBXE overlay priority bits....................................................................................................................324

Table 89: VBXE attribute map block layout.........................................................................................................325

Table 90: VBXE blitter setup block......................................................................................................................327

Table 91: VBXE blit modes.................................................................................................................................328

Table 92: VBXE blitter speeds............................................................................................................................329

Table 93: VBXE registers....................................................................................................................................331

Table 94: Bit-3 Full-View 80 $D508 register bits.................................................................................................338

Table 95: Measured signal levels for sync and all luminances............................................................................426

Table 96: NTSC saturation ratios........................................................................................................................428

Table 97: Measured artifacting delays................................................................................................................432

Table 98: CPU opcode table...............................................................................................................................448

Index of Figures

Figure 1: System Block Diagram..........................................................................................................................26

Figure 2: Effects of overlapping IRQ/NMI timing...................................................................................................45

Figure 3: Effect of vertical scrolling on mode lines................................................................................................68

- 7 Altirra Hardware Reference ManualCreated by Avery Lee

Figure 4: Abusing vertical scrolling in the "GTIA 9++" mode.................................................................................70

Figure 5: ANTIC event timing................................................................................................................................92

Figure 6: DMA and CPU timing for DLI handler....................................................................................................94

Figure 7: POKEY detailed timer timing...............................................................................................................105

Figure 8: POKEY asynchronous serial receive timing.........................................................................................113

Figure 9: POKEY synchronous serial receive/transmit timing.............................................................................114

Figure 10: CX-75 triggering glitch on NTSC 800XL............................................................................................149

Figure 11: Veronica memory layout.....................................................................................................................195

Figure 12: SIO command timing.........................................................................................................................202

Figure 13: Ultimate1MB flash memory map........................................................................................................314

Figure 14: YIQ/YUV color space relations..........................................................................................................424

Figure 15: Effect of color correction on computed palette...................................................................................429

Figure 16: Altirra NTSC high artifacting pipeline.................................................................................................435

Figure 17: Altirra PAL high artifacting pipeline.....................................................................................................439

Figure 18: Analog audio block model.................................................................................................................441

Figure 19: Decay from second stage amplifier....................................................................................................443

Figure 20: Dynamic clamping effect....................................................................................................................444

- 8 Altirra Hardware Reference ManualCreated by Avery Lee Copyright © 2009-2023 Avery Lee, All Rights Reserved.

Permission is granted to redistribute this document in verbatim form as long as it is done free of charge and for

non-commercial purposes. All trademarks are the property of their respective owners.

While the information in this document is presumed correct, no guarantee is provided as to its accuracy or

fitness for a particular use. - 9 Altirra Hardware Reference ManualCreated by Avery Lee

1.1Introduction

This document describes the hardware programming model used by Altirra, an emulator for the Atari 8-bit series

of home computers, including the 400, 800, 600XL, 800XL, 1200XL, 130XE, and XEGS models. Although the

emulator provides a virtual programming environment, it is intended to mimic the actual hardware. This

document attempts to describe the hardware in detail as the target to which the emulator aspires to imitate.

Some of this information has been collected from both official and unofficial sources, and some of it has been

determined by hand through testing on a real, still functioning Atari 800XL.

While I've spent a lot of time tracking down details myself, I have to acknowledge the substantial amount of

literature already available which provided background for this document. First and foremost, I'm indebted to the

technical staff behind the Atari Home Computer System Hardware Manual, which did a very good job of

describing the behavior and programming specifications for the official functionality in the Atari hardware, and

which should be considered required reading prior to this document. Similar shout-outs go to the authors of

Atari's OS Manual, which similarly documents the software side, and to Ian Chadwick and his Mapping the Atari,

Revised Edition, which contains the most detailed and complete memory map of the Atari I know of.

If you have the time and inclination, please check out my Altirra emulator, available at the following web address.

You can also find the latest version of this manual there. http://www.virtualdub.org/altirra.html -- Avery Lee

1.1 - Introduction10

Altirra Hardware Reference ManualCreated by Avery Lee

1.2What's new in this edition

This release

•Accessories ◦Stack Lightpen. •Cartridges ◦SIDE 2: Added missing CF select bit. •Serial I/O bus

◦Fixed typo in protocol diagram that showed 10-18 ms for the ACK-to-data delay instead of 1.0-1.8

ms. ◦1030: Additional timing and dialing information. •Disk drives ◦Happy 1050: Detailed memory map and additional caching behavior. ◦XF551: Added third firmware version between 7.4 and 7.7. ◦Added 1450XLD parallel disk drive. •Parallel Bus Interface ◦MIO: Fixed description of $D1FE bit 4, which controls SEL and not MSG. ◦MIO: Fixed inverted IRQ status bits. ◦Added 1400XL/1450XLD V: and T: devices.

2022-11-29 release

•Disk drives ◦Added info about XF551 firmware rev. 7.4 and 7.7 differences. ◦Added US Doubler firmware information. •POKEY ◦More details on initialization mode. ◦Expanded on many audio topics.

◦Rotated around some of the noise generator patterns to canonically start from initialization state.

◦Cycle-precise timer behavior, including STIMER and AUDF1-4 write timing.

2022-07-07 release

•Fixed some typos referring to the PIA chip number as 6522 instead of 6520. •CPU

1.1 - Introduction11

Altirra Hardware Reference ManualCreated by Avery Lee

◦Fixed typo regarding B flag, which is pushed set on the stack for a BRK and cleared for IRQ/NMI.

•ANTIC

◦Fixed typo in Display list > Suspended display list DMA: the last IR byte is repeated when display list

DMA is disabled.

◦Fixed incorrect /RNMI timing - it only needs to be asserted across one leading edge of VBLANK, not

two. •Accessories ◦Expanded information on light pens. ◦Added ComputerEyes Video Acquisition System. •Disk drives ◦Added info on 1050 firmware revision E.

2022-01-03 release

•ANTIC ◦Refresh row address counter is not cleared on reset. •Disk drives

◦Clarified receive timing for Happy 1050 and added info about error handling when track buffering is

enabled. ◦Added step timing for Speedy 1050. •Parallel Bus Interface ◦Corrected reserved ranges for PBI ($D6xx and D7xx instead of $D5xx and D6xx). •Appendices ◦Added appendix on physical tape format.

2021-10-02 release

•System architecture ◦Added brief overview of top-level system architecture. •CPU ◦Expanded discussion of flags. •ANTIC ◦Fixed erroneous starting cycles for playfield DMA in the text (the charts were correct). •POKEY ◦Clarified some details about counter timing and distortion selection. ◦Added section on two-tone counter timing. •Accessories

1.1 - Introduction12

Altirra Hardware Reference ManualCreated by Avery Lee ◦Note on XEP80 baud rate limits, row advance timing anomaly, and delete line behavior. •Cartridges ◦New section on SIDE 3. •Serial I/O bus ◦New section on 820 Printer. •Disk drives

◦Removed Indus GT from list of disk drives that do not update PERCOM block on density detection.

◦Expanded information on PERCOM disk drive firmware revisions. •Physical disk format ◦Added measured capture range for bit cell periods. •Reference ◦Fixed swapped mode reference for the CHBASE register. ◦Fixed missing POTGO register in register listing.

2020-10-23 release

•Disk drives ◦Fixed swapped PB0 and PB7 definitions for 1050 drives. ◦Added behavior of various drives with no disk inserted. ◦Clarified FDC handling of the head/side address field value. ◦Added firmware revision information for 1050, Indus GT, and Percom RFD. ◦Added Atari 815. ◦Added Percom AT88-S1 and AT88-SPD. •Internal devices ◦Added Bit-3 Full-View 80. ◦Added Atari 1090 80 Column Video Card.

2019-12-30 release

•System control ◦Fixed a typo in the PAL clock rate. •ANTIC ◦Timing and behavior for the 400/800 System Reset NMI, even on XL/XE computers. •GTIA

◦Clarified listed behavior for mode 9 combining with the fifth player (PF3) and for mode 11 regarding

unusual COLBK values.

1.1 - Introduction13

Altirra Hardware Reference ManualCreated by Avery Lee •POKEY ◦Fixed a typo in the keyboard layout for the Return key. •Disk drives ◦Fixed 810 port B entries being listed in reversed order. ◦Added information on the 810 Turbo, Astra 1001 / The "One", and Amdek AMDC-I/II.quotesdbs_dbs21.pdfusesText_27

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