7721 datasheet(415/577 Pages) RENESAS

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APPLICATION

7721 Group User’s Manual

16–12

16.1 Memory connection

(3)

Precautions on memory connection

As described in to below, if specifications of the external memory do not match those of the

M37721, some considerations must be incorporated into circuit design:

When using an external memory that requires a long access time

When data is output from an external memory before falling edge of the E signal

When using an external memory that outputs data for more than tpzx(E-DLZ/DHZ) after rising edge of

the E signal

When using external memory that requires long access time

If the M37721’s tsu(DL/DH-E) cannot be satisfied because the external memory requires a long access

time, try to carry out the following:

q Lower f(XIN).

q Select “software Wait is inserted.” (Refer to section “3.2 Software Wait.”)

q Use Ready function. (Refer to section “3.3 Ready function.”)

Figure 16.1.9 shows an example of using Ready function (no software Wait). Figure 16.1.10 shows

an example of using Ready function (software Wait).

Ready function is valid for the internal areas, so that the circuits in Figures 16.1.9 and 16.1.10 use

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the chip select signal (CS2) to specify areas where Ready function is valid. In these cases, the CS2

signal is externally generated.

7721 Datasheet(PDF) 415 Page - Renesas Technology Corp