Advertisement
is 33221100 where every two bits specifies the most significant two colour bits for the
specified square.
Figure 3-3. 4x4 tile group layout. Adapted from [20].
The NES only has 2 KB to store name tables and attribute tables, allowing it to store two of
each. However it can address up to four of each. Mirroring is used to allow it to do this. There
are four types of mirroring which are described below, using abbreviations for logical name
tables (those that can be addressed), L1 at $2000, L2 at $2400, L3 at $2800 and L4 at
$2C00:
Horizontal mirroring maps L1 and L2 to the first physical name table and L3 and L4 to the
second as shown in figure 3-4.
Vertical mirroring maps L1 and L3 to the first physical name table and L2 and L4 to the
second as shown in figure 3-5.
Square 0
Square 1
$0
$1
$4
$2
$3
$6
Square 2
Square 3
$8
$9
$C
$A
$B
$E
1
1
2
2
Figure 3-4. Horizontal mirroring.
1
2
1
2
Figure 3-5. Vertical mirroring.
20
$5
$7
$D
$F
Advertisement
