Commodore Amiga - Page 259

BLTAFWM
BLTALWM
BLTxDAT
BLTDDAT
address point to the start of the next line. Each
source or destination has its own modulo, allowing
each to be a different size, while an identical
area of each is used in the bUtter operation.
LINE DRAW BLTAMOD and BLTBMOD are used as slope
LINE DRAW storage registers and must be preloaded
LINE DRAW with the values (4Y-4X) and (4Y)
LINE DRAW respectively. Y/X= line slope.
LINE DRAW BLTCMOD and BLTDMOD must both be
LINE DRAW pre loaded with the width (in bytes)
LINE DRAW of the image into which the line is
LINE DRAW being drawn (normally two times the
LINE DRAW screen width in words) •
044 W A Blitter first-word mask for source A
046
W A Blitter last-word mask for source A
The
patterns in these two registers are ANDed with
the first and last words of each line of data from
source A into the bUtter. A zero in any bit
overrides data from source A. These registers
should be set to all Is for fill mode or for
line-drawing mode.
074
W A Blitter source x data register
This register holds source x (x=A,B,C) data for
use by the bUtter. It is normally loaded by the
bUtter DMA channel; however, it may also be
preloaded by the microprocessor.
LINE DRAW BLTADAT is used as an index register
LINE DRAW and must be preloaded with 8000.
LINE DRAW BLTBDAT is ,used for texture; it must
LINE DRAW be preloaded with E'E' if no texture
LINE DRAW (soUd line) is desired.
Blitter destination data register
This register holds the data resulting from each
word of blitter operation until it is sent to a
RAM destination. This ,is a dllllll1Y address and
cannot be read by the micro. The transfer is
automatic during blitter operation.
BLTCONO 040 W A BUtter control register 0
BLTCONI 042 W A Blitter control register 1
These two control registers are used together to
control bUtter operations. There are two basic
modes, area and line, which are selected by bit
o of BLTCONl, as shown below.
AREA MJDE ("normal")
-------------------------
BI1'# BLTCONO
BLTCON1
---- -------
15 ASH3
BSH3
14 ASH2
BSH2
13 ASH!
BSH1
12 ASAO
BSHO
11
USEA
X
10
USEB
X
09
USEC
X
08
USED
X
07
LE'7
X
06
LE'6
X
05
LE'S
X
04
LE'4
EFE
03 LE'3
IE'E
02
LE'2 E'CI
01
LE'1
DESC
00
LE'O
LINE (=0)
ASH3-0
BSH3-0
USEA
USEB
USEC
USED
LE'7-0
EFE
IFE
E'CI
DESC
LINE
Shift value of A source
Shift value of B source
Mode control bit to use source A
Mode control bit to use source B
Mode control bit to use source C
Mode control bit to use destination D
Logic function mlnterm select lines
Exclusive fill enable
Inclusive fill enable
Fill carry input
Descending (decreasing address) control bit
Line mode control bit (set to 0)
LINE DRAW
LINE MODE (line draw)
LINE DRAW
------------------------------
LINE DRAW
BI1'# BLTCONO
BLTCONI
LINE DRAW
---- -------
LINE DRAW 15 START3
TEXTURE3
LINE DRAW
14 START2
TEXTURE2
LINE DRAW
13 START1
TEXTUREI
LINE DRAW 12
STARTO
TEXTUREO
LINE DRAW
11
1
0
LINE DRAW
10
0
0
LINE DRAW 09
1
0
LINE DRAW
08
1
0
LINE DRAW
07 LE'7
0
LINE DRAW
06 LE'6
SIGN
LINE DRAW
05
LE'S
o (Reserved)
LINE DRAW
04
LE'4
SUD
LINE DRAW 03
LE'3
SUL
LINE DRAW 02
LE'2
AUL
LINE DRAW 01
LE'1
SING
LINE DRAW
00 LE'O
LINE (=1)
LINE DRAW