AMD Geode LX 800@0.9W - Manual (Page 291)

AMD Geode™ LX Processors Data Book 291
Display Controller 33234H
6.5.5.4 Read Modes
There are two read modes provided to assist the CPU with
graphics operations in planar modes. Read mode 0 simply
returns the frame buffer data. Read mode 1 allows the CPU
to do a single color compare across eight pixels. Figure 6-
18 shows the data flow for read modes. Figure 6-19 on
page 292 shows how the color compare logic in Figure 6-
18 works.
Figure 6-18. Read Mode Data Flow
Memory Read Data [31:0]
Read Map Select [1:0]
Chain2
Chain4
CPU A[1:0]
Select Read
Map Logic
ReadMode1 B
CPU Read Data [7:0]
In [31:0]
Out [7:0]
Color Compare
In [31:0]
Out [7:0]
Color Compare [3:0]
Color Don’t Care [3:0]
A B
Logic