Blitter control register 0
These two control registers are used together to control blitter operations. There are 2 basic modes, are and line, which are selected by bit 0 of BLTCON1, as show below.
| AREA MODE Bit | BLTCON0 | BLTCON1 | LINE MODE Bit | BLTCON0 | BLTCON1 |
|---|---|---|---|---|---|
| 15 | ASH3 | BSH3 | 15 | ASH3 | BSH3 |
| 14 | ASH2 | BSH2 | 14 | ASH2 | BSH2 |
| 13 | ASH1 | BSH1 | 13 | ASH1 | BSH1 |
| 12 | ASA0 | BSH0 | 12 | ASH0 | BSH0 |
| 11 | USEA | 0 | 11 | 1 | 0 |
| 10 | USEB | 0 | 10 | 0 | 0 |
| 09 | USEC | 0 | 09 | 1 | 0 |
| 08 | USED | 0 | 08 | 1 | 0 |
| 07 | LF7 | DOFF | 07 | LF7 | DPFF |
| 06 | LF6 | 0 | 06 | LF6 | SIGN |
| 05 | LF5 | 0 | 05 | LF5 | OVF |
| 04 | LF4 | EFE | 04 | LF4 | SUD |
| 03 | LF3 | IFE | 03 | LF3 | SUL |
| 02 | LF2 | FCI | 02 | LF2 | AUL |
| 01 | LF1 | DESC | 01 | LF1 | SING |
| 00 | LF0 | LINE(=0) | 00 | LF0 | LINE(=1) |
| Function | Description |
|---|---|
| ASH3-0 | Shift value of A source |
| BSH3-0 | Shift value of B source and line texture |
| USEA | Mode control bit to use source A |
| USEB | Mode control bit to use source B |
| USEC | Mode control bit to use source C |
| USED | Mode control bit to use destination D |
| LF7-0 | Logic function minterm select lines |
| EFE | Exclusive fill enable |
| IFE | Inclusive fill enable |
| FCI | Fill carry input |
| DESC | Descending (dec address)control bit |
| LINE | Line mode control bit |
| SIGN | Line draw sign flag |
| OVF | Line/draw r/l word overflow flag |
| SUD | Line draw, Sometimes up or down (=AUD) |
| SUL | Line draw, Sometimes up or left |
| AUL | Line draw, Always up or left |
| SING | Line draw, Single bit per horiz line |
| DOFF | Disables the D output- for external ALUs The cycle occurs normally, but the data bus is tristate (hires chips only) |
Calculation of LF7->LF0 copy mask
| Bit | Ch A | Ch B | Ch C | Example expected on D |
|---|---|---|---|---|
| LF0 | 0 | 0 | 0 | 0 |
| LF1 | 0 | 0 | 1 | 0 |
| LF2 | 0 | 1 | 0 | 0 |
| LF3 | 0 | 1 | 1 | 0 |
| LF4 | 1 | 0 | 0 | 1 |
| LF5 | 1 | 0 | 1 | 1 |
| LF6 | 1 | 1 | 0 | 1 |
| LF7 | 1 | 1 | 1 | 1 |
Result for BLTCON0 %11110000=$f0 => 'move.w #$??f0,BLTCON0(a6)'