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Chapter 31 External Bus
3.Setting Example of the Chip Select Area
3. Setting Example of the Chip Select AreaIn the external bus interface, a total of eight chip select areas can be set.This section presents an example of setting the chip select area.

■Example of Setting the Chip Select Area

The address space of each area can be placed, in units of a minimum of 64 KB, anywhere in the 4 GB space
using ASR0-7 (Area Select Registers) and ACR0-7 (Area Configuration Registers). When bus access is made to
an area specified by these registers, the corresponding chip select signals (CS0-CS7) are activated (L output)
during the access cycle.

●Example of setting ASRs and ASZ3-0

• ASR1=0003H ACR1 ASZ3-0=0000B: Chip select area 1 is assigned to 00030000H to 0003FFFFH.
• ASR2=0FFCH ACR2 ASZ3-0=0010B: Chip select area 2 is assigned to 0FFC0000H to 10000000H.
• ASR3=0011H ACR3 SZ3-0=0100B: Chip select area 3 is assigned to 00100000H to 00200000H.
Since at this point 1 MB is set for bits ASZ3-0 of the ACR, the unit for boundaries 1 MB and bits 19-16 of ASR3
are ignored. Before there is any writing to ACR0 after a reset, 00000000H-FFFFFFFFHis assigned to chip select
area 0.
Set the chip select areas so that there is no overlap.
Figure 3-1 "Example of Setting the Chip Select Area" shows an example of setting the chip select area.
Figure 3-1 Example of Setting the Chip Select Area
(Initial value) (Example)
00000000H00000000H
00030000HArea 1 64 KB
00040000H
Area 0 00100000H
Area 3 1 MB
00200000H
0FFC0000H
0FFFFFFFH
Area 2 256 KB
FFFFFFFFHFFFFFFFFH