6.4.3
BREQ
Input Timing
After driving the
BREQ
pin low, hold it low until
BACK
goes low. If
BREQ
returns to the high
level before
BACK
goes low, the bus arbiter may operate incorrectly.
To terminate the external-bus-released state, hold the
BREQ
signal high for at least three states.
If
BREQ
is high for too short an interval, the bus arbiter may operate incorrectly.
6.4.4 Transition To Software Standby Mode
If contention occurs between a transition to software standby mode and a bus request from an
external bus master, the bus may be released for one state just before the transition to software
standby mode (see figure 6-23). When using software standby mode, clear the BRLE bit to 0 in
BRCR before executing the SLEEP instruction.
Figure 6-23 Contention between Bus-Released State and Software Standby Mode
146
ø
Address bus
Strobe
BREQ
BACK
Bus-released state
Software standby mode
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