7733 datasheet(735/940 Pages) RENESAS

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APPLICATIONS

7735 Group User’s Manual

17–9

(2) Timing for writing data

Figure 17.1.4 shows the timing for writing data to an external memory.

When data is written, the data is output from when an interval of td(WE-DQ) has passed after signal

____ ____

WEL/WEH’s

falling edge until an interval of th(WE-DQ) has passed after signal WEL/WEH’s rising edge.

td(WE-DQ) is a constant which is independent of f(XIN); th(WE-DQ) is a constant which is dependent on

f(XIN). Table 17.1.4 lists the value of td(WE-DQ) and the calculation formula for th(WE-DQ).

Make sure that the data output timing for writing data satisfies the following specifications of the

external memory: data setup time (tsu(D)) and data hold time (th(D)) for writing data.

Fig. 17.1.4 Timing at which data is written to external memory

Table 17.1.4 Value of td(WE-DQ) and calculation formula for th(WE-DQ) (Unit: ns)

Wait 0

Wait 1

– 22

1 ! 109

2•f(f2)

No wait

0 or 1

Wait bit: Bit 2 at address 5E16

Wait selection bit: Bit 0 at address 5F16

Note: The above is applied when the system clock selection bit (bit 3 at address 6C16) = “0.”

Software wait

Wait bit

Wait selection bit

td(WE-DQ)

th(WE-DQ)

External memory

write signals

W, WE

External memory

chip select signals

CE, S

(The others are specifications of

external memory.)

: Specifications of

the 7735 Group

g This is applied when the external data bus

= 16 bits wide (BYTE = “L” ).

WEL, WEH

Address and data output

A0/D0 to A7/D7

/D8 to A15/D15

tsu(D)

th(D)

Address

Data

Address

tw(WE)

th(WE-DQ)

td(WE-DQ)

17.1 Memory expansion

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