7751 Datasheet, PDF (376/540 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATIONS
17.1 Memory expansion
(3) Precautions on memory expansion
As described in Œ to Ž below, if specifications of the external memory do not match those of the
M37751, some considerations must be incorporated into circuit design as in the following cases:
ΠWhen using an external memory that requires a long access time, ta(AD)
_

When
using
an
external
memory
that
outputs
data
within
tpxz(E-P1Z/P2Z)
after
falling
of
the
E
signal
_
Ž When using an external memory that outputs data for more than tpzx(E-P1Z/P2Z) after rising of the E
signal
ΠWhen using an external memory that requires a long access time, ta(AD)
If the M37751’s tsu(P1D/P2D-E) cannot be satisfied because the external memory requires a long access
time, t , a(AD) examine the method described below:
q Lower f(XIN).
q Select a long bus cycle by software. (Refer to section “12.2 Bus cycle.”)
q Use Ready function. (Refer to section “12.3 Ready function.”)
Figure 17.1.8 shows an example of using Ready function (at 2φ access in low–speed running ).
Figure 17.1.9 shows an example of using Ready function (at 3φ access in low–speed running ).
Figure 17.1.10 shows an example of using Ready function (at 3φ access in high–speed running ).
Figure 17.1.11 shows an example of using Ready function (at 4φ access in high–speed running ).
Ready function is available _{_}fo_{_}r_{_} the internal areas, so that the circuit in Figures 17.1.8 to 17.1.11
use the chip select signal (CS2) to specify the area where Ready function is available.
7751 Group User’s Manual
17–11