Atmel Evaluation Kit AT91SAM9G25-EK AT91SAM9G25-EK Data Sheet
Product codes
AT91SAM9G25-EK
409
SAM9G25 [DATASHEET]
11032D–ATARM–10-Mar-2014
29.11.1 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.
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.
cycles during which the data bus remains busy after the rising edge of NCS.
illustrates the Data Float Period in NRD-controlled mode (READ_MODE =1), assuming a data float period
of 2 cycles (TDF_CYCLES = 2).
shows the read operation when controlled by NCS (READ_MODE = 0) and
the TDF_CYCLES parameter equals 3.
Figure 29-20.TDF Period in NRD Controlled Read Access (TDF = 2)
NBS0, NBS1,
NBS2, NBS3,
A0, A1
NBS2, NBS3,
A0, A1
NCS
NRD controlled read operation
tpacc
MCK
NRD
D[31:0]
TDF = 2 clock cycles
A[25:2]