44
Mitsubishi microcomputers
M16C / 62P Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Memory Space Expansion Function
development
Preliminary Specifications Rev.1.0
Specifications in this manual are tentative and subject to change.
Memory Space Expansion Function
The following describes a memory space extension function.
During memory expansion or microprocessor mode, the memory space expansion function allows the
access space to be expanded using the appropriate register bits.
Table 1.8.1 shows the way of setting memory space expansion function, memory spaces.
Table 1.8.1. The Way of Setting Memory Space Expansion Function, Memory Space
Memory space expansion function
1 Mbytes mode
4 Mbytes mode
How to set (PM15 to PM14)
00
2
11
2
Memory space
1 Mbytes (no expansion)
4 Mbytes
(1) 1 Mbyte Mode
In this mode, the memory space is 1 Mbytes. In 1 Mbyte mode, the external area to be accessed is
specified using the CSi (i = 0 to 3) signals (hereafter referred to as the CSi area). Figures 1.8.2 to 1.8.3
show the memory mapping and CS area in 1 Mbyte mode.
(2) 4 Mbyte Mode
In this mode, the memory space is 4 Mbytes. Figure 1.8.1 shows the DBR register. The BSR2 to BSR0
bits select a bank number which is to be accessed to read or write data. Setting the OFS bit to “1” (with
offset) allows the accessed address to be offset by 40000
16
.
In 4 Mbyte mode, the CSi (i=0 to 3) pin functions differently for each area to be accessed.
Addresses 04000
16
to 3FFFF
16
, C0000
16
to FFFFF
16
The CSi signal is output from the CSi pin (same operation as 1 Mbyte mode. However the last address
of CS1 area is 3FFFF
16
)
Addresses 40000
16
to BFFFF
16
The CS0 pin outputs “L”
The CS1 to CS3 pins output the value of the BSR2 to BSR0 bits (bank number)
Figures 1.8.4 to 1.8.5 show the memory mapping and CS area in 4 Mbyte mode. Note that banks 0 to 6
are data-only areas. Locate the program in bank 7 or the CSi area.
Figure 1.8.1. DBR Register
Data bank register (Note)
Symbol
DBR
Address
000B
16
After reset
00
16
Bit name
Description
Bit symbol
RW
b7
b6
b5
b4
b3
b2
b1
b0
OFS
Offset bit
0: Not offset
1: Offset
BSR0
Bank selection bits
0 1 0: Bank 2
1 0 0: Bank 4
1 1 0: Bank 6
0 1 1: Bank 3
1 0 1: Bank 5
1 1 1: Bank 7
Nothing is assigned. When write, set to “0”. When read, its content is
“0”.
Nothing is assigned. When write, set to “0”. When read, its content is
“0”.
b5 b4 b3
b5 b4 b3
RW
RW
BSR1
BSR2
(b1-b0)
(b7-b6)
RW
RW
Note : Effective when the PM01 to PM00 bits are set to “01
2
” (memory expansion mode) or “11
2
” (microprocessor
mode).