Altirra Hardware Reference Manual 2020-10-23 Edition Avery Lee Altirra Hardware Reference Manual Created by Avery Lee Table of Contents 1.1 . Introduction .............................................................................................................................................. 9 1.2 . What's new in this edition ...................................................................................................................... 10 1.3 . Conventions in this manual .................................................................................................................... 14 1.4 . Concepts ................................................................................................................................................ 15 2 . CPU .............................................................................................................................................................. 18 2.1 . Registers ................................................................................................................................................ 19 2.2 . Decimal mode ........................................................................................................................................ 19 2.3 . Cycle timing ........................................................................................................................................... 20 2.4 . Interrupts ................................................................................................................................................ 22 2.5 . Undocumented instructions ................................................................................................................... 25 2.6 . 65C02 compatibility ............................................................................................................................... 28 2.7 . 65C816 compatibility ............................................................................................................................. 30 2.8 . 65C816 new features ............................................................................................................................. 31 2.9 . Examples ............................................................................................................................................... 33 2.10 . Further reading .................................................................................................................................... 34 3 . System control .............................................................................................................................................. 35 3.1 . System Reset button ............................................................................................................................. 36 3.2 . Peripheral Interface Adapter (PIA) ......................................................................................................... 36 3.3 . Memory system ..................................................................................................................................... 38 3.4 . Bank switching ....................................................................................................................................... 40 3.5 . Extended memory .................................................................................................................................. 40 3.6 . Miscellaneous connections .................................................................................................................... 43 3.7 . Examples ............................................................................................................................................... 43 3.8 . Further reading ...................................................................................................................................... 44 4 . ANTIC ........................................................................................................................................................... 45 4.1 . Basic operation ...................................................................................................................................... 46 4.2 . Display timing ........................................................................................................................................ 47 4.3 . Playfield ................................................................................................................................................. 48 4.4 . Character modes ................................................................................................................................... 49 4.5 . Mapped (bitmap) modes ........................................................................................................................ 51 4.6 . Display list .............................................................................................................................................. 52 4.7 . Scrolling ................................................................................................................................................. 55 4.8 . Non-maskable interrupts ........................................................................................................................ 60 4.9 . WSYNC ................................................................................................................................................. 62 4.10 . VCOUNT .............................................................................................................................................. 64 4.11 . Playfield DMA ....................................................................................................................................... 64 4.12 . Abnormal playfield DMA ....................................................................................................................... 66 4.13 . Player/missile DMA .............................................................................................................................. 71 4.14 . Scan line timing ................................................................................................................................... 71 4.15 . Cycle counting example ....................................................................................................................... 82 4.16 . Examples ............................................................................................................................................. 84 4.17 . Further reading .................................................................................................................................... 85 5 . POKEY ......................................................................................................................................................... 86 5.1 . Addressing ............................................................................................................................................. 87 5.2 . Initialization ............................................................................................................................................ 87 5.3 . Sound generation .................................................................................................................................. 87 5.4 . Serial port .............................................................................................................................................. 90 5.5 . Clock generation .................................................................................................................................... 98 5.6 . Noise generators ................................................................................................................................... 98 5.7 . Interrupts ................................................................................................................................................ 99 - 2 Altirra Hardware Reference Manual Created by Avery Lee 5.8 . Keyboard scan ..................................................................................................................................... 101 5.9 . Paddle scan ......................................................................................................................................... 105 5.10 . Examples ........................................................................................................................................... 106 5.11 . Further reading ................................................................................................................................... 107 6 . CTIA/GTIA .................................................................................................................................................. 108 6.1 . Color encoding ..................................................................................................................................... 109 6.2 . Artifacting .............................................................................................................................................. 111 6.3 . Player/missile graphics ........................................................................................................................ 113 6.4 . Collision detection ...............................................................................................................................