R01UH0136EJ0210 Rev.2.10
Page 161 of 800
Jul 31, 2012
M16C/64A Group
12. Memory Space Expansion Function
In the example below, the
CS
pin of a 4-MB ROM is connected to the MCU’s
CS0
pin. The 4-MB ROM
address input pins AD21, AD20, and AD19 are connected to the MCU’s
CS3
,
CS2
, and
CS1
pins,
respectively. The address input AD18 pin is connected to the MCU’s A19 pin. Figure 12.6 to Figure 12.8
show the relationship of addresses between the 4-MB ROM and the MCU in the connection example of
Figure 12.5.
In microprocessor mode or memory expansion mode, where the PM13 bit in the PM1 register is 0,
banks are located every 512 KB. Setting the OFS bit in the DBR register to 1 (offset) allows the
accessed address to be offset by 40000h, allowing even data overlapping at a bank boundary to be
accessed in succession.
In memory expansion mode, where the PM13 bit is 1, each 512-KB bank can be accessed in 256 KB
units by switching them with the OFS bit.
Because the SRAM can be accessed when the chip select signals S2 is high and
S1
is low,
CS0
and
CS2
can be connected to S2 and
S1
, respectively. If SRAM does not have the input pins that accept
high active and low active chip select signals (
S1
, S2),
CS0
and
CS2
should be decoded externally to
the chip.
Figure 12.5
External Memory Connection Example in 4-MB Mode
17
8
MCU
D0 to D7
A0 to A16
A17
RD
WR
CS1
CS2
CS3
CS0
A19
4-
MB R
O
M
DQ0 to DQ7
AD0 to AD16
AD17
AD18
AD19
OE
CS
12
8-
KB
SR
A
M
DQ0 to
DQ7
AD0 to
AD16
S2
W
OE
S1
AD20
AD21
Note:
1. If only one chip select pin (S1 or S2) is present, use an external circuit for decoding.
(1)
Содержание M16C/60 Series
Страница 853: ...M16C 64A Group R01UH0136EJ0210...