CONNECTION WITH EXTERNAL DEVICES
7902 Group User’s Manual
3-27
3.2 Chip select wait controller
(3) Recovery cycle
As the recovery cycle, 1 or 2 cycles of
φ1 can be selected by both the recovery cycle insert select bit
and the recovery-cycle-insert number select bit. (See Figures 3.2.2, 3.2.3, and 3.2.5). Insertion of
recovery cycles allows devices with longer output disable time at read to be connected without using
bus buffers.
Since addresses are maintained throughout recovery cycles, devices requiring longer address hold
time can easily be connected; on the other hand, by inserting 2 recovery cycles to extend the data
hold time at write by 1 cycle of
φ1, devices requiring longer data hold time can also be connected.
Figures 3.2.14 and 3.2.15 show operating waveforms at recovery cycle insertion.
Fig. 3.2.14 Operating waveforms at recovery cycle insertion (1)
RD
BLW,BHW
Write Data
Access to
area CSi
φ1
CSi
ALE
A
B
A
A + 1
<No recovery cycle inserted>
Access to
internal area
16-bit data is accessed starting
from an odd-numbered address
in area CSi.
(a) At read/write of data
g If area CSi where recovery cycles have been inserted at the preceding bus cycle is accessed, the same recovery cycles will also be inserted here.
A0 to A23
Access to
area CSi
φ1
CSi
ALE
A
A + 1
<1 recovery cycle inserted>
Access to
internal area
16-bit data is accessed starting from an
odd-numbered address in area CSi.
B
Recovery
cycle
Recovery
cycle
Recovery
cycle
(Next bus
cycle)
A0 to A23
g
Access to
area CSi
A
A + 1
<2 recovery cycles inserted>
Access to
internal area
16-bit data is accessed starting from an odd-
numbered address in area CSi.
B
Recovery
cycle
Recovery
cycle
Recovery
cycle
(Next bus
cycle)
g
φ1
ALE
A
A + 2
A + 4
A + 6
<No recovery cycle inserted>
RD
(b) At instruction prefetch (Normal access; quadruple consecutive access)
g If area CSi where recovery cycles have been inserted at the preceding bus cycle is accessed, the same recovery cycles will also be inserted here.
Notes 1: This applies when the external data bus width = 16 bits. When 8 bits, each address is incremented by 1.
2: When the same area CSi is consecutively accessed, pin CSi outputs “L” level consecutively.
CSi
(Note 2)
A0–A23
(Note 1)
A
A + 2
A + 6
<1 recovery cycle inserted>
A + 4
Recovery
cycle
(Next bus cycle)
g
A
A + 2
A + 6
<2 recovery cycles inserted>
A + 4
Recovery
cycle
(Next bus cycle)
g
Write Data
Data
RD
BLW,BHW
Write Data
φ1
CSi
ALE
A0 to A23
RD
BLW,BHW
φ1
ALE
RD
CSi
(Note 2)
A0–A23
(Note 1)
φ1
ALE
RD
CSi
(Note 2)
A0–A23
(Note 1)