schematics:megadrive1bapinout
Bus Arbiter
The Bus Arbiter is just there to keep things clean and to stop processors treading on each other's toes. There's a fair few pins I've no idea what the function is for. Suggestions are welcome!
| Pin | Name | Description | - | Pin | Name | Description |
|---|---|---|---|---|---|---|
| 1 | GND | Ground | - | 51 | MCLK | Master Clock input |
| 2 | - | Unknown | - | 52 | - | Unknown |
| 3 | - | Unknown | - | 53 | - | Unknown |
| 4 | - | Unknown | - | 54 | - | Unknown |
| 5 | VA8 | 68K Address 8 | - | 55 | - | Unknown |
| 6 | VA9 | 68K Address 9 | - | 56 | !SOUND | YM-2612 !CS |
| 7 | VA10 | 68K Address 10 | - | 57 | ZCLK | Z80 clock |
| 8 | VA11 | 68K Address 11 | - | 58 | !WRES | Reset button input |
| 9 | VA12 | 68K Address 12 | - | 59 | !ZRAM | Z80 memory !CE |
| 10 | VA13 | 68K Address 13 | - | 60 | !REF | Unknown |
| 11 | VA14 | 68K Address 14 | - | 61 | !M1 | Z80 !M1 |
| 12 | VA15 | 68K Address 15 | - | 62 | !ZRES | Z80 Reset |
| 13 | VA16 | 68K Address 16 | - | 63 | !ZBR | Z80 !BUSRQ |
| 14 | VA17 | 68K Address 17 | - | 64 | !WAIT | Z80 !WAIT |
| 15 | VA18 | 68K Address 18 | - | 65 | !ZBAK | Z80 !BUSAK |
| 16 | VA19 | 68K Address 19 | - | 66 | !ZWR | Z80 !WR |
| 17 | VA20 | 68K Address 20 | - | 67 | !ZRD | Z80 !RD |
| 18 | VA21 | 68K Address 21 | - | 68 | !IREQ | Z80 !IREQ |
| 19 | VA22 | 68K Address 22 | - | 69 | !MREQ | Z80 !MREQ |
| 20 | VA23 | 68K Address 23 | - | 70 | !NMI | Z80 !NMI |
| 21 | FC0 | 68K FC0 | - | 71 | ZA0 | Z80 Address 0 |
| 22 | FC1 | 68K FC1 | - | 72 | ZA7 | Z80 Address 7 |
| 23 | !VPA | 68K !VPA | - | 73 | ZA8 | Z80 Address 8 |
| 24 | !VRES | 68K !Reset | - | 74 | ZA9 | Z80 Address 9 |
| 25 | !HALT | 68K !HALT | - | 75 | ZA10 | Z80 Address 10 |
| 26 | VD8 | 68K Data 8 | - | 76 | ZA11 | Z80 Address 11 |
| 27 | - | Unknown | - | 77 | - | Unknown |
| 28 | - | Unknown | - | 78 | - | Unknown |
| 29 | - | Unknown | - | 79 | - | Unknown |
| 30 | VCLK | 68K Clock | - | 80 | ZA12 | Z80 Address 12 |
| 31 | GND | Ground | - | 81 | ZA13 | Z80 Address 13 |
| 32 | !TIME | Unknown | - | 82 | ZA14 | Z80 Address 14 |
| 33 | !CAS0 | I/O !CAS0 | - | 83 | ZA15 | Z80 Address 15 |
| 34 | !DTAK | 68K !DTAK | - | 84 | ZD00 | Z80 Data 0 |
| 35 | R/!W | 68K R/!W | - | 85 | !FDWR | Unknown |
| 36 | !LDS | 68K !LDS | - | 86 | - | Unknown |
| 37 | !VDS | 68K !UDS | - | 87 | !ROM | Unknown |
| 38 | !AS | 68K !AS | - | 88 | !ASEL | Unknown |
| 39 | !INTAK | VDP !INTAK | - | 89 | !CAS2 | Unknown |
| 40 | - | Unknown | - | 90 | - | Unknown |
| 41 | !VDPM | Unknown | - | 91 | !RAS2 | VDP !RAS2 |
| 42 | !BG | 68K !BG | - | 92 | !CE0 | Unknown |
| 43 | !BGAK | 68K !BGACK | - | 93 | !VTOV | I/O !VTOV |
| 44 | !BR | 68K !BR | - | 94 | !ZTOV | I/O !ZTOV |
| 45 | !EOE | 68K memory 2 !OE | - | 95 | !SRES | I/O !SRES |
| 46 | IA14 | Unknown | - | 96 | !IO | I/O !IO |
| 47 | !NOE | 68K memory 1 !OE | - | 97 | !M3 | I/O !M3 |
| 48 | EDCL | HSCLK | - | 98 | !CART | Cartridge presence |
| 49 | !OE0 | x | - | 99 | - | Unknown |
| 50 | !HSYNC | !HSYNC from VDP | - | 100 | - | Unknown |
There's some supply pins that are marked as unknown, solely because I developed a headache whilst doing this!
schematics/megadrive1bapinout.txt · Last modified: 2019/08/27 20:45 by 127.0.0.1