
17-8
BitBLT Registers
`efmp69030 Databook
Revision 1.3 11/24/99
23
BitBLT Engine Color Depth Control Select
0: Bits 5 and 4 of the BitBLT Configuration Register (XR20) are used to configure the
BitBLT engine for one of three color depths. This is the default after reset.
1: Bits 25 and 24 of this register are used to configure the BitBLT engine for one of three
color depths.
22-20 Pattern Vertical Alignment
Specifies which scanline’s worth (i.e., which 1 of the 8 horizontal rows) of the 8x8 pattern
data will appear in the first scanline’s worth of the destination output data. Depending on
the location of the destination, the upper left corner of the upper left tile of the pattern data
is usually aligned with the upper left corner of the destination output data as the pattern data
is tiled into the destination. The BitBLT engine determines the horizontal alignment of the
leftmost tiles of pattern data relative to the destination using the lower order bits of the
destination address specified in BR07. However, the vertical alignment relative to the
destination must be specified using these 3 bits.
19
Solid Pattern Select
Note: This bit applies only when the pattern data is monochrome (determined by bit 18 of
this register).
0: Causes monochrome pattern data to actually be read and used as is normal, if indeed
monochrome pattern data is being used as an input to a BitBLT operation.
1: Causes the BitBLT engine to forgo the process of reading the pattern data. Instead, the
presumption is made that all of the bits of the pattern data are set to 0. The pattern operand
for all bit-wise operations is forced to the background color specified in BR01.
18
Pattern Color Depth
0: Specifies that the pattern data is in color and therefore can have a color depth of 8, 16,
or 24 bits per pixel.
1: Specifies that the pattern data is monochrome and therefore has a color depth of 1 bit
per pixel.
17
Monochrome Pattern Write-Masking
Note: This bit applies only when the pattern data is monochrome (determined by bit 18 of
this register).
This bit enables a form of per-pixel write-masking in which monochrome pattern data is
used as a pixel mask that controls which pixels at the destination will be written to by the
BitBLT engine.
0: This disables the use of monochrome pattern data as a write mask, allowing normal
operation of the BitBLT engine with regard to the use of monochrome pattern data.
1: Wherever a bit in monochrome pattern data carries the value of 0 the byte(s) of the
corresponding pixel at the destination are NOT written, thereby preserving any data already
carried by those bytes.