Commodore Amiga A500 Technical Reference Manual page 207

L l N E
DRAW: BLTADAT is used as an index register and must be pre-
loaded with 8000. BLTBDAT is used for texture. It
must be preloaded with FF if no texture (solid line) is
desired.
BLTDDAT
Blitter destination data register
This register holds the data resulting from each word of Blitter oper-
ation until it is sent to a
RAM
destination. This is a dummy address
and cannot be read by the micro. The transfer is automatic during
Blitter operation.
BLTCONO
Blitter control register
0
BLTCON l
Blitter control register
1
These two control registers are used together to control Blitter op-
erations. There are 2 basic modes, area and line, which are selected
by bit 0 of BLTCON 1, as shown below.
AREA MODE ("normal")
BIT#
1 5
14
1 3
12
11
10
09
08
07
06
0 5
04
03
0 2
0 1
00
ASH3-0
BSH3-0
USEA
USEB
USEC
USED
LF7-0
EFE
I FE
FCI
DESC
LlNE
BLTCONO BLTCON 1
ASH3 BSH3
ASH2 BSH2
ASH l BSH l
ASAO BSHO
USEA
X
USEB
X
USEC
X
USED
X
LF7
X
LF6
X
LF5
X
LF4 EFE
LF3 IFE
LF2 FCI
LF 1 DESC
LFO LINE(= 0)
Shift value of
A
source
Shift value of
B
source
Mode control bit to use Surce
A
Mode control bit to use Source
B
Mode control bit to use Source C
Mcde control
bit
to
use Destination
D
Logic function minterm select lines
Exclusive
fill
enable
Inclusive
fill
enable
Fill
carry input
Descending (decreasing address)
control bit
Line mode control bit (set to 0)