BLTCON0

         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 ("normal")     | LINE MODE (line draw)     |
         +------+---------+---------+------+---------+----------+
         | BIT# | BLTCON0 | BLTCON1 | 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(ABC)| DOFF    | 07   | LF7(ABC)| DPFF     |
         | 06   | LF6(ABc)| 0       | 06   | LF6(ABc)| SIGN     |
         | 05   | LF5(AbC)| 0       | 05   | LF5(AbC)| OVF      |
         | 04   | LF4(Abc)| EFE     | 04   | LF4(Abc)| SUD      |
         | 03   | LF3(aBC)| IFE     | 03   | LF3(aBC)| SUL      |
         | 02   | LF2(aBc)| FCI     | 02   | LF2(aBc)| AUL      |
         | 01   | LF1(abC)| DESC    | 01   | LF1(abC)| SING     |
         | 00   | LF0(abc)| LINE(=0)| 00   | LF0(abc)| LINE(=1) |
         +------+---------+---------+------+---------+----------+


         ASH 3-0 Shift value of A source
         BSH 3-0 Shift value of B source
         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
         LF 7-0 Logic function minterm select lines
         EFE Exclusive fill enable
         IFE Inclusive fill enable
         FCI Fill carry input
         DESC Descending (decreasing address) control bit
         LINE Line mode control bit (set to 0 on normal mode)
         DOFF      Disables the D output- for external ALUs
                   The cycle occurs normally, but the data
                   bus is tristate (hires chips only)


         LINE DRAW      LINE MODE (line draw)
         LINE DRAW
         LINE DRAW    BIT# BLTCON0  BLTCON1
         LINE DRAW
         LINE DRAW     15   START3  TEXTURE3
         LINE DRAW     14   START2  TEXTURE2
         LINE DRAW     13   STARTl  TEXTURE1
         LINE DRAW     12   START0  TEXTURE0
         LINE DRAW     11   1       0
         LINE DRAW     10   0       0
         LINE DRAW     09   1       0
         LINE DRAW     08   1       0
         LINE DRAW     07   LF7     0
         LINE DRAW     06   LF6     SIGN
         LINE DRAW     05   LF5     0 (Reserved)
         LINE DRAW     04   LF4     SUD
         LINE DRAW     03   LF3     SUL
         LINE DRAW     02   LF2     AUL
         LINE DRAW     01   LF1     SING
         LINE DRAW     00   LF0     LINE(=1)
         LINE DRAW
         LINE DRAW     START 3-0 Starting point of line
         LINE DRAW               (0 thru 15 hex)


         LINE DRAW     LF7-0 Logic function minterm
         LINE DRAW     select lines should be preloaded
         LINE DRAW     with 4A to select the equation
         LINE DRAW     D=(AC+ABC). Since A contains a
         LINE DRAW     single bit true (8000), most bits
         LINE DRAW     will pass the C field unchanged
         LINE DRAW     (not A and C), hut one bit will
         LINE DRAW     invert the C field and combine it
         LINE DRAW     with texture (A and B and not C).
         LINE DRAW     The A bit is automatically moved
         LINE DRAW     across the word by the hardware.
         LINE DRAW
         LINE DRAW     LINE Line mode control bit (set to 1)
         LINE DRAW     SIGN Sign flag
         LINE DRAW     0 Reserved for new mode
         LINE DRAW     SING Single bit per horizontal line for
         LINE DRAW     use with subsequent area fill
         LINE DRAW     SUD Sometimes up or down (=AUD*)
         LINE DRAW     SUL Sometimes up or left
         LINE DRAW     AUL Always up or left


         LINE DRAW     The 3 bits above select the octant
         LINE DRAW     for line drawing:


         LINE DRAW     OCT     SUD SUL AUL
         LINE DRAW
         LINE DRAW      0       1   1   0
         LINE DRAW      1       0   0   1
         LINE DRAW      2       0   1   1
         LINE DRAW      3       1   1   1
         LINE DRAW      4       1   0   1
         LINE DRAW      5       0   1   0
         LINE DRAW      6       0   0   0
         LINE DRAW      7       1   0   0


         LINE DRAW The "B" source is used for
         LINE DRAW texturing the drawn lines.


SEE ALSO: Blitter programming