M69000 Asiliant Technologies, M69000 Datasheet - Page 344

• Manufacturer Part Number: M69000
• Manufacturer: Asiliant Technologies

Specifications of M69000

• Lead Free Status / Rohs Status: Supplier Unconfirmed

BitBLT Operation
E-9
The BitBLT engine reads from the source and writes to the destination starting with the left-most pixel in the
top-most line of both, as shown in step (a). As shown in step (b), corruption of the source data has already
started with the copying of the top-most line in step (a) — part of the source that originally contained lighter-
colored pixels has now been overwritten with darker-colored pixels. More source data corruption occurs as
steps (b) through (d) are performed. At step (e), another line of the source data is read, but the two right-
most pixels of this line are in the region where the source and destination locations overlap, and where the
source has already been overwritten as a result of the copying of the top-most line in step (a). Starting in
step (f), darker-colored pixels can be seen in the destination where lighter-colored pixels should be. This
errant effect occurs repeatedly throughout the remaining steps in this BitBLT operation. As more lines are
copied from the source to the destination, it becomes clear that the end result is not as originally intended.
The BitBLT engine can be programmed to alter the order in which source data is read and destination data
is written when necessary to avoid the kind of source data corruption problem illustrated earlier. Bits 8 and
9 of BR04 provide the ability to change the point at which the BitBLT engine begins reading and writing data
from the upper left-hand corner (the usual starting point) to one of the other three corners. In other words,
through the use of these two bits, the BitBLT engine may be set to read data from the source and write it to
the destination starting at any of the four corners of the panel. The following figure shows how this feature
can be used to perform the same BitBLT operation illustrated earlier, but without corrupting the source data.
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69000 Databook
Subject to Change Without Notice
Revision 1.3 8/31/98