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(3) Precautions on memory expansion
As described in
M37751, some considerations must be incorporated into circuit design as in the following cases:
When using an external memory that requires a long access time, t
When using an external memory that outputs data within t
When using an external memory that outputs data for more than t
signal
When using an external memory that requires a long access time, t
If the M37751's t
time, t
, examine the method described below:
a(AD)
Lower f(X
).
IN
Select a long bus cycle by software. (Refer to section "12.2 Bus cycle.")
Use Ready function. (Refer to section "12.3 Ready function.")
Figure 17.1.8 shows an example of using Ready function (at 2 φ access in low–speed running ).
Figure 17.1.9 shows an example of using Ready function (at 3 φ access in low–speed running ).
Figure 17.1.10 shows an example of using Ready function (at 3 φ access in high–speed running ).
Figure 17.1.11 shows an example of using Ready function (at 4 φ access in high–speed running ).
Ready function is available for the internal areas, so that the circuit in Figures 17.1.8 to 17.1.11
use the chip select signal (CS
to
below, if specifications of the external memory do not match those of the
cannot be satisfied because the external memory requires a long access
su(P1D/P2D-E)
___
) to specify the area where Ready function is available.
2
7751 Group User's Manual
APPLICATIONS
17.1 Memory expansion
a(AD)
after falling of the E signal
pxz(E-P1Z/P2Z)
after rising of the E
pzx(E-P1Z/P2Z)
a(AD)
_
_
17–11
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