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Bus-released state
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ø
RFSH
Refresh
request
BACK
Figure 7-24 Refresh Cycles when Bus is Released
•
If a bus cycle is prolonged by insertion of wait states, the first refresh request is held, as in the
bus-released state.
•
If there is contention with a bus request from an external bus master when making a transition
to software standby mode, a one-state bus-released state may occur immediately before the
transition to software standby mode (see figure 7-25).
When using software standby mode, clear the BRLE bit to 0 in BRCR before executing the
SLEEP instruction.
When making a transition to self-refresh mode, the strobe waveform output may not be
guaranteed due to the same kind of contention. This, too, can be prevented by clearing the
BRLE bit to 0 in BRCR.
ø
BREQ
BACK
Address bus
Strobe
Figure 7-25 Contention between Bus-Released State and Software Standby Mode
Refresh cycle
External bus
Software standby mode
released state
184
CPU cycle
Refresh cycle
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