Datasheet

SAM9261 [DATASHEET]
Atmel-6062O-ATARM-SAM9261-Datasheet_21-Jun-16
172
20.10.1 READ_MODE
Setting the READ_MODE to 1 indicates to the SMC that the NRD signal is responsible for turning off the tri-state
buffers of the external memory device. The Data Float Period then begins after the rising edge of the NRD signal
and lasts TDF_CYCLES MCK cycles.
When the read operation is controlled by the NCS signal (READ_MODE = 0), the TDF field gives the number of
MCK cycles during which the data bus remains busy after the rising edge of NCS.
Figure 20-20 illustrates the Data Float Period in NRD-controlled mode (READ_MODE =1), assuming a data float
period of 2 cycles (TDF_CYCLES = 2). Figure 20-21 shows the read operation when controlled by NCS
(READ_MODE = 0) and the TDF_CYCLES parameter equals 3.
Figure 20-20. TDF Period in NRD Controlled Read Access (TDF = 2)
NBS0, NBS1,
NBS2, NBS3,
A0, A1
NCS
NRD controlled read operation
tpacc
MCK
NRD
D[31:0]
TDF = 2 clock cycles
A[25:2]