7733 datasheet(414/940 Pages) RENESAS

414 / 940 page

APPLICATIONS

7733 Group User’s Manual

17–7

17.1.3 Points in memory expansion

(1) Timing for reading data

Figure 17.1.4 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 the external

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

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

Table 17.1.3 lists the value of tpxz(E-DZ) and the calculation formula for tpzx(E-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.”)

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

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

collides with the head of address.

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

ten(OE)

Address

tpzx(E-DZ)

tsu(D-E)

ta(OE)

ta(CE), ta(S)

tDF, tdis(OE)

g 2

g 3

tw(EL)

Data

tpxz(E-DZ)

ten(CE), ten(S)

External memory

data output

External memory

output enable signal

(Read signal)

External memory

chip select signals

CE, S

Address output

and data input

/D8 to A15/D15

A16/D0 to A23/D7

g 1

: Specifications

of the 7733 Group

(The others are specifications of

external memory.)

Fig. 17.1.4 Timing at which data is read from external memory

17.1 Memory expansion

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