ReSource 2021 ReSource 2021 SOME INFORMATION ON THE MTX THAT I WISH I’D HAD IN THE 1980’S…. MARTIN ALLCORN BILL BRENDLING 1 ReSource 2021 0 CONTENTS 1 Introduction .......................................................................................................................................... 5 2 Under the hood ..................................................................................................................................... 6 3 The Memory Map ................................................................................................................................. 8 3.1 Rom Enabled Mode ....................................................................................................................... 8 3.2 CPM Mode .................................................................................................................................. 10 3.3 The 256k Series 2 ........................................................................................................................ 11 3.4 SDX Memory ............................................................................................................................... 12 3.5 Using Paged Memory .................................................................................................................. 12 3.6 Memory Map in BASIC ................................................................................................................ 14 3.6.1 Low RAM ............................................................................................................................. 14 3.6.2 Middle RAM ........................................................................................................................ 14 3.6.3 High RAM ............................................................................................................................ 15 3.7 BASIC Program ............................................................................................................................ 15 3.8 Machine Code in BASIC ............................................................................................................... 16 3.8.1 Numeric value ..................................................................................................................... 16 3.8.2 Statement label ................................................................................................................... 17 3.8.3 Data Definitions .................................................................................................................. 17 3.8.4 Comment............................................................................................................................. 17 3.9 Relocating Machine Code ........................................................................................................... 17 3.10 BASIC Variables ........................................................................................................................... 18 3.10.1 Virtual Addresses ................................................................................................................ 18 3.10.2 List of Variable Names ........................................................................................................ 18 3.10.3 List of Variable Values ......................................................................................................... 19 3.10.4 Array Data ........................................................................................................................... 20 3.11 NODDY Pages .............................................................................................................................. 20 3.12 SDX Basic Disc Operating System (BDOS) ................................................................................... 20 3.13 NODE Ring ................................................................................................................................... 22 3.13.1 Node Names List ................................................................................................................. 27 3.13.2 Transmit Command Block ................................................................................................... 27 3.14 CFX Video .................................................................................................................................... 27 4 The Video System ................................................................................................................................ 29 2 ReSource 2021 4.1 Display Control Codes ................................................................................................................. 29 4.1.1 Control Codes ...................................................................................................................... 29 4.1.2 Escape Codes ....................................................................................................................... 30 4.2 Accessing the Display via RST 10 and RST 28 .............................................................................. 31 4.3 MTX ROM Routines Involved in Displaying Characters .............................................................. 35 4.3.1 PRINTX (0CABh) ................................................................................................................... 35 4.3.2 GETSTR (00BCh) .................................................................................................................. 35 4.3.3 BSLOAD (1:3A6Fh) ............................................................................................................... 35 4.3.4 CONSTR (1:3ABAh) .............................................................................................................. 36 4.3.5 DEVSP (1:3AEAh) ................................................................................................................. 36 4.3.6 GETCH (1:2F9Bh) ................................................................................................................. 36 4.3.7 DISP1 (1:2FA6h) .................................................................................................................. 36 4.3.8 PRTCH (1:2FDBh) ................................................................................................................. 37 4.3.9 SCENTR (00CBh) .................................................................................................................. 37 4.3.10 SCENT (1876h) ..................................................................................................................... 37 4.4 Accessing the VDP directly .......................................................................................................... 39 4.5 Text Mode ................................................................................................................................... 42 4.6 Graphics 2 Mode ......................................................................................................................... 45 4.6.1 Graphics 2 in text mode ...................................................................................................... 48 4.7 Sprites from BASIC ...................................................................................................................... 50 5 The CTC ............................................................................................................................................... 51 5.1 125hz Interrupt ........................................................................................................................... 52 5.1.1 So why 125Hz? .................................................................................................................... 53 5.1.2 MTX BASIC and Interrupts ................................................................................................... 53 5.2 Baud Rate Clocks ......................................................................................................................... 53 5.3 VDP interrupt .............................................................................................................................. 54 5.4 Interrupt priority ......................................................................................................................... 54 6 The PSG ............................................................................................................................................... 56 6.1 PSG registers ............................................................................................................................... 56 6.2 Driving the PSG ........................................................................................................................... 57 6.3 Sound Envelopes from BASIC ...................................................................................................... 59 7 The keyboard ...................................................................................................................................... 60 7.1 Reset keys ................................................................................................................................... 60 3 ReSource 2021 7.2 The main keyboard ..................................................................................................................... 60 7.3 Keyboard Re-Mapping ...............................................................................................................