7641 datasheet(260/385 Pages) RENESAS

260 / 385 page

Rev.2.00

Aug 28, 2006

page 129 of 148

7641 Group

REJ09B0336-0200

APPLICATION

2.10 External devices connection

(2) External memory connection example : RDY function (one wait) in use

Outline: RDY function is used because the external memory has a slow-memory-access speed.

Specifications:

•In read/write status of the CPU, input “L” to the RDY(P30) pin will cause extension

of 1 to 3

φ cycles on its read/write cycle.

•When the slow memory wait select bit (b1, b0) is = “01”, it is extended by one

cycle.

______ ______

•RD/WR signal holds “L” level during the extended time.

•Usable RAM and ROM at f(XIN) = 24 MHz, Vcc = 5 V are given bellow:

- OE access time : ta(OE)

≤ 107 ns

- Data setup time at write : tsu(D)

≤ 100 ns

- Examples satisfying these specifications: M5M27C256AK-10 (EPROM),

M5M5256BP-10 (SRAM)

Figure 2.10.10 shows the RDY function use example, and Figures 2.10.11 to 2.10.13 show the read

and write cycles.

7641 Group

AD15

AD14

AD0

EPROM

CNVss

P31, P32

DB0

DB7

SRAM

A0 to A14

D0 to D7

A0 to A14

DQ1 to DQ8

74F04

M5M27C256AK-10

Vcc = 4.15 to 5.25 V

24 MHz

Memory map

000016

SFR area

External RAM area

000816

001016

007016

047016

800016

FFFF16

M5M256BP

SFR area

Internal RAM area

External RAM area

External ROM area

RDY

Fig. 2.10.10 RDY function use example

7641 Datasheet(PDF) 260 Page - Renesas Technology Corp

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