Renesas 7700 FAMILY, User Manual

Page: 373 / 540

APPLICATIONS
7751 Group User’s Manual
17–8
17.1 Memory expansion
17.1.3 Points in memory expansion
(1) Reading data
Figure 17.1.6 shows the timing at which data is read from an external memory.
When reading data, the external data bus is placed in a floating state, and data is read from the
_
external memory. This floating state is maintained from t
pxz(E–P1Z/P2Z)
after falling of the E signal till
_
t
pzx(E–P1Z/P2Z)
after rising of the E signal. Table 17.1.3 lists the values of t
pxz(E–P1Z/P2Z)
and the formulas
to calculate t
pzx(E–P1Z/P2Z)
.
Consider timing during data read to avoid collision between the data being read–in and the preceding
or following address output because the external data bus is multiplexed with the external address
bus. (Refer to “(3) Precautions on memory expansion.”)
Fig. 17.1.6 Timing at which data is read from external memory
External memory
data output
✽
1: This applies when the external data bus has a width of 16 bits (BYTE = “L”).
External memory
output enable signal
(Read signal)
OE
E
External memory
chip select signal
CE, S
✽
2: If one of the external memory’s specifications is smaller than
t
pxz
(E-P1Z/P2Z)
, there is a possibility of the tail of
→
Refer to “(3) Precautions on memory expansion.”
✽
3: If one of the external memory’s specifications is greater than
t
pzx
(E-P1Z/P2Z)
data colliding with the head of address.
→
Refer to “(3) Precautions on memory expansion.”
Address output and data input
A
8
/
D
8
–A
15
/D
15
A
16
/D
0
–A
23
/D
7
✽
1
t
en
(OE)
Address
t
pzx
(E-P1Z/P2Z)
t
su
(P1D/P2D-E)
: Specifications of the M37751
(The others are the external
memory’s.)
t
a
(OE)
t
a
(CE)
, t
a
(S)
t
DF
, t
dis
(OE)
✽
2
✽
3
t
w(EL)
Data
t
pxz
(E-P1Z/P2Z)
t
en
(CE)
, t
en
(S)
Address
, there is a possibility of the tail of
address colliding with the head of data.