SAM9M11_14 Datasheet, PDF (192/1488 Pages) ATMEL Corporation – Atmel | SMART ARM-based Embedded MPU

20.8.2 Read Mode
As NCS and NRD waveforms are defined independently of one other, the SMC needs to know when the read data
is available on the data bus. The SMC does not compare NCS and NRD timings to know which signal rises first.
The READ_MODE parameter in the SMC_MODE register of the corresponding chip select indicates which signal
of NRD and NCS controls the read operation.
20.8.2.1 Read is Controlled by NRD (READ_MODE = 1):
Figure 20-10 shows the waveforms of a read operation of a typical asynchronous RAM. The read data is available
t_PACC after the falling edge of NRD, and turns to ‘Z’ after the rising edge of NRD. In this case, the READ_MODE
must be set to 1 (read is controlled by NRD), to indicate that data is available with the rising edge of NRD. The
SMC samples the read data internally on the rising edge of Master Clock that generates the rising edge of NRD,
whatever the programmed waveform of NCS may be.
Figure 20-10. READ_MODE = 1: Data is sampled by SMC before the rising edge of NRD
MCK
A[25:2]
NBS0,NBS1,
NBS2,NBS3,
A0, A1
NRD
NCS
D[31:0]
t_PACC
Data Sampling
20.8.2.2 Read is Controlled by NCS (READ_MODE = 0)
Figure 20-11 shows the typical r ead cycle of an LCD module. The read data is valid t_PACC after the falling edge of
the NCS signal and remains valid until the rising edge of NCS. Data must be sampled when NCS is raised. In that
case, the READ_MODE must be set to 0 (read is controlled by NCS): the SMC internally samples the data on the
rising edge of Master Clock that generates the rising edge of NCS, whatever the programmed waveform of NRD
may be.
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SAM9M11 [DATASHEET]
Atmel-6437F-ATARM-SAM9M11-Datasheet_21-Oct-14