Download Renesas PCA4738L-64A Technical information

APPLICATION
2.4 Processor mode
(2) Application example of memory expansion in the case where the ONW (One-Wait)
function is used
Outline : ONW function is used when the external memory access is slow.
If “L” level signal is input to the P32 /ONW pin while the CPU is in the read or write status,
the read or write cycle corresponding to 1 cycle of φ is extended. In the extended period,
the RD or WR signal is kept at the “L” level. The ONW function operates only when data is
read from or written into addresses 000016 to 000716 and addresses 0440 16 to FFFF 16 .
Figure 2.4.7 shows an application example of the ONW function.
3800 group
CNVSS
AD15
2
74F04
M5M27C256AK-10
P30, P3 1
ONW
8
P4
CE
M5M5256BP-10
S
AD14
–
15
A0–A14
A0–A14
AD0
EPROM
8
P5
DB0
–
8
D0–D7
DB7
8
OE
SRAM
DQ1–DQ8
OE
Memory map
0000 16 External RAM area
P6
(M5M5256BP)
000816
SFR area
004016 Internal RAM area
RD
WR
2
W
044016 External RAM area
P7
(M5M5256BP)
8MHz
VCC= 5.0V ± 10 %
800016
External ROM area
FFFF16
(M5M27C256AK)
____
Fig. 2.4.7 Application example of the ONW function
3800 GROUP USER’S MANUAL
2-53