Atmel SAM9X25, Manual

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29.12.2 Frozen Mode
When the external device asserts the NWAIT signal (active low), and after internal synchroniza-
tion of this signal, the SMC state is frozen, i.e., SMC internal counters are frozen, and all control
signals remain unchanged. When the resynchronized NWAIT signal is deasserted, the SMC
completes the access, resuming the access from the point where it was stopped. See
Figure 29-
26 . This mode must be selected when the external device uses the NWAIT signal to delay the
access and to freeze the SMC.
The assertion of the NWAIT signal outside the expected period is ignored as illustrated in Figure
29-27 .
Figure 29-26. Write Access with NWAIT Assertion in Frozen Mode (EXNW_MODE = 10)
EXNW_MODE = 10 (Frozen)
WRITE_MODE = 1 (NWE_controlled)
NWE_PULSE = 5
NCS_WR_PULSE = 7
A
[25:2]
MCK
NWE
NCS
4 3 2 1 1 1 0 1
4 5 6 3 2 2 2 2 1 0
Write cycle
D[31:0]
NWAIT
FROZEN STATE
NBS0, NBS1,
NBS2, NBS3,
A0,A1
internally synchronized
NWAIT signal