The image planes on the CRX-48Z consist of two buffers with
24 planes each. Each buffer consists of three banks, one each for
red, green, and blue. Each of the 4 image color maps on the CRX-48Z
consists of three color tables — one each for red, green,
and blue. Regardless of which color map mode is currently being
used, the data in each of the banks is used as an index into a color
table for that color of bank. For example, the pixel value in the
red bank is used as an index into the red color table to determine
the intensity of red that should be displayed for that pixel.
As a result of this color map organization, frame buffer configurations
that are of depth 8 require that the 8 bits of pixel data be written
to all three banks in order for the correct RGB values to be displayed.
A bank_switch
in depth 8 (CMAP_NORMAL)
frame buffer configurations selects which of the two 24-plane buffers
will be accessed for block_read
and block_write.
For more information on the bank_switch
command, read the section "Changes to bank_switch()"
in Chapter 1.
Using a bank number of 0 selects the first of the two buffers.
This first buffer is the bank currently enabled for writing as selected
by the double_buffer/dbuffer_switch.Using
a bank number of 1 selects the second buffer.
block_write
duplicates the pixel value to the three banks of the current buffer.
block_read returns
values in the red bank (which should be the same as the values in
the green and blue banks).
bank_switch
in depth 24 (CMAP_FULL)
frame buffer configurations selects which one of the six 8-plane
banks will be accessed for block_write
and block_read.
Please note: In the following table, "current writable buffer"
is defined as the buffer selected by double_buffer/dbuffer_switch.
Table 5-1 Bank
Selection
wbank | bank selected |
|---|
0 | red bank, current writable buffer |
1 | green bank, current writable buffer |
2 | blue bank, current writable buffer |
3 | red bank, non-writable buffer |
4 | green bank, non-writable buffer |
5 | blue bank, non-writable buffer |
6 | Z-buffer [1] |
Printable version
