3 ready mode – Rainbow Electronics AT91CAP9S250A User Manual
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196
6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
22.11.3
Ready Mode
In Ready mode (EXNW_MODE = 11), the SMC behaves differently. Normally, the SMC begins
the access by down counting the setup and pulse counters of the read/write controlling signal. In
the last cycle of the pulse phase, the resynchronized NWAIT signal is examined.
If asserted, the SMC suspends the access as shown in
and
. After
deassertion, the access is completed: the hold step of the access is performed.
This mode must be selected when the external device uses deassertion of the NWAIT signal to
indicate its ability to complete the read or write operation.
If the NWAIT signal is deasserted before the end of the pulse, or asserted after the end of the
pulse of the controlling read/write signal, it has no impact on the access length as shown in
.
Figure 22-28. NWAIT Assertion in Write Access: Ready Mode (EXNW_MODE = 11)
EXNW_MODE = 11 (Ready mode)
WRITE_MODE = 1 (NWE_controlled)
NWE_PULSE = 5
NCS_WR_PULSE = 7
A
[25:2]
MCK
NWE
NCS
4
3
2
1
0
0
0
4
5
6
3
2
1
1
1
0
Write cycle
D[31:0]
NWAIT
internally synchronized
NWAIT signal
Wait STATE
NBS0, NBS1,
NBS2, NBS3,
A0,A1