NEC uPD72257, Preliminary User'S Manual

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8.5.3.2 Limiter operation
The Drawing Engine contains six limiters. Each limiter contains four registers:
• DRWLnSTART
• DRWLnXADD
• DRWLnYADD
The value register is not visible to the user and is just an internal register which is
then output. It is possible to drive the limiters in a threshold mode. Then all values
above 0 are considered 1. This is used in case antialiasing is not desired (e.g. for
shared edges).
Note In the diagram below following abbreviations are used:
• start = DRWLnSTART
• xadd = DRWLnXADD
• yadd = DRWLnYADD
x=0
y=0
xadd=a
yadd=b
start=c
value=start
output value
x<width
x=x+1 Value=value+xadd
y<height
y=y+1
start=start+yadd
End
Begin
yes
no
yes
Figure 8-9 Flowchart of linear limiter operation
Drawing Engine Chapter 8
Preliminary User's Manual S19203EE1V3UM00
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