7733 datasheet(733/940 Pages) RENESAS

733 / 940 page

APPLICATIONS

7735 Group User’s Manual

17–7

17.1.3 Points in memory expansion

(1) Timing for reading data

Figure 17.1.3 shows the timing at which data is read from an external memory.

When data is read, the external data bus enters a floating state and reads data from an external

memory. The floating state of the external data bus is retained from when an interval of tpxz(RDE-DZ)

____

has passed after signal RDE’s falling edge until an interval of tpzx(RDE-DZ) has passed after signal

____

RDE’s

rising edge. tpxz(RDE-DZ) is a constant which is independent of f(XIN); tpzx(RDE-DZ) is a constant

which is dependent on f(XIN). Table 17.1.3 lists the value of tpxz(RDE-DZ) and the calculation formula

for tpzx(RDE-DZ).

Note that the external data bus is multiplexed with the external address bus. Therefore, when reading

data, it is necessary to consider timing to avoid collision between data being read-in and an address

which is output preceding or following the data. (Refer to “(3) Precautions on memory expansion.”)

Fig. 17.1.3 Timing at which data is read from external memory

ten(OE)

Address

tpzx(RDE-DZ)

tsu(D-RDE)

ta(OE)

ta(CE), ta(S)

tDF, tdis(OE)

g 2

g 3

tw(RDE)

Data

tpxz(RDE-DZ)

ten(CE), ten(S)

External memory

data output

g 1 This is applied when the external data bus = 16 bits wide (BYTE = “L”).

External memory

output enable signal

(Read signal)

RDE

External memory

chip select signals

CE, S

g 2 When the external memory’s specifications are smaller than tpxz(RDE-DZ), there is a possibility that the tail of an

address collides with the head of data.

→ Refer to “(3) Precautions on memory expansion.”

g 3 When the external memory’s specifications are greater than tpzx(RDE-DZ), there is a possibility that the tail of

data collides with the head of an address.

→ Refer to “(3) Precautions on memory expansion.”

Address output

/D0 to A7/D7

A8/D8 to A15/D15

g 1

: Specifications

of the 7735 Group

(The others are specifications of

external memory.)

17.1 Memory expansion

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