7702 Datasheet, PDF (340/522 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
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
tpxz(E–P1Z/P2)
after
the
falling
edge
of
the
E
signal till tpzx(E–P1Z/P2Z) after the rising edge of the E signal. Table 17.1.4 lists the values of tpxz(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.”)
tw(EL)
E
External memory
output enable signal
OE
(Read signal)
External memory
chip select signal
CE, S
Address output and data input
A8/D8–A15/D15 ^V1
A16/D0–A23/D7
Address
tpxz(E-P1Z/P2Z)
ta(OE)
ta(CE), ta(S)
V2
ten(OE)
External memory
data output
ten(CE), ten(S)
Data
tpzx(E-P1Z/P2Z)
Address
tDF, tdis(OE) ^V3
tsu(P1D/P2D-E)
: Specifications of the M37702
(The others are specifications of
V1 This applies when the external data bus has a width of 16 bits (BYTE = “L”). ^{external memory.)}
V2 If one of the external memory’s specifications is smaller than tpxz(E-P1Z/P2Z) , there is a possibility of the tail of
address colliding with the head of data. → Refer to “(3) Precautions on memory expansion.”
V3 If one of the external memory’s specifications is greater than tpzx(E-P1Z/P2Z) ,there is a possibility of the tail of
data colliding with the head of address. → Refer to “(3) Precautions on memory expansion.”
Fig. 17.1.6 Timing at which data is read from an external memory
17–8
7702/7703 Group User’s Manual