SH7032 Datasheet, PDF (156/687 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

Section 8 Bus State Controller (BSC)
Table 8.8 A26–A24 Bits and Chip Select Signals
Address
A26
A25
A24
0
0
0
1
1
0
1
1
0
0
1
1
0
1
Area Selected
Area 0
Area 1
Area 2
Area 3
Area 4
Area 5
Area 6
Area 7
Chip Select Pin Driven Low
CS0
CS1
CS2
CS3
CS4
CS5
CS6
CS7
The chip select signal is output only for external accesses. When accessing the on-chip ROM (area
0), on-chip supporting modules (area 5), and on-chip RAM (area 7), the CS0, CS5, and CS7 pins
are not driven low. When accessing DRAM space (area 1), select the RAS and CAS signals with
the pin function controller.
8.3.4 Shadows
The size of each area is 16 Mbytes, which can be specified with the 24 address bits A23–A0 for 8-
bit spaces and 16-bit spaces alike. Bits A23 and A22, however, output externally only when the
address multiplex function is used in DRAM space (area 1); in all other cases, there is no output,
so the actually accessible area for all areas is the 4 Mbytes that can be specified with the 22 bits
A21–A0. Regardless of the values of A23 and A22, the same 4 Mbytes of actual space is accessed.
As illustrated in figure 8.4 (a), the A23 and A22 bit regions 00, 01, 10 and 11 are called shadows
of actual areas. Shadows are allocated in 4-Mbyte units for both 8-bit and 16-bit bus widths. When
the same addresses H'3200000, H'3600000, H'3A00000 and H'3E00000 are specified for values
A21–A0, as shown in figure 8.4 (b), the same actual space is accessed regardless of the A23 and
A22 bits.
In areas whose bus widths are switchable using the A27 address bit, the shadow of the same actual
space is allocated to both A27 = 0 spaces and A27 = 1 spaces (figure 8.4(a)). When the value of
A27 is changed, the valid AD pins switch from AD15–AD0 to AD7–AD0, but the actual space
accessed remains the same.
The spaces of on-chip ROM (area 0), DRAM (area 1), on-chip supporting modules (area 5), and
on-chip RAM (area 7) have shadows of different sizes from those mentioned above. See section
8.3.5, Area Descriptions, for details.
Rev. 7.00 Jan 31, 2006 page 130 of 658
REJ09B0272-0700