SAM4CM_14 Datasheet, PDF (524/1177 Pages) ATMEL Corporation – Atmel | SMART ARM-based Flash MCU

27.13.4 NWAIT Latency and Read/Write Timings
There may be a latency between the assertion of the read/write controlling signal and the assertion of the NWAIT
signal by the device. The programmed pulse length of the read/write controlling signal must be at least equal to
this latency plus the 2 cycles of resynchronization + 1 cycle. Otherwise, the SMC may enter the hold state of the
access without detecting the NWAIT signal assertion. This is true in Frozen mode as well as in Ready mode. This
is illustrated on Figure 27-29.
When EXNW_MODE is enabled (ready or frozen), the user must program a pulse length of the read and write
controlling signal of at least:
minimal pulse length = NWAIT latency + 2 resynchronization cycles + 1 cycle
Figure 27-29. NWAIT Latency
MCK
A[23:0]
NRD
4
3
2
1
0
minimal pulse length
WAIT STATE
0
0
NWAIT
intenally synchronized
NWAIT signal
NWAIT latency 2 cycle resynchronization
Read cycle
EXNW_MODE = 10 or 11
READ_MODE = 1 (NRD_controlled)
NRD_PULSE = 5
524
SAM4CM Series [DATASHEET]
Atmel-11203C-ATARM-SAM4CM32-SAM4CM16-SAM4CM8-Datasheet_06-Oct-14