Atmel SAM4S Xplained Pro Starter Kit Atmel ATSAM4S-XSTK ATSAM4S-XSTK Data Sheet
Product codes
ATSAM4S-XSTK
397
SAM4S [DATASHEET]
11100E–ATARM–24-Jul-13
26.8.1.4 Null Delay Setup and Hold
If null setup and hold parameters are programmed for NRD and/or NCS, NRD and NCS remain active continuously in
case of consecutive read cycles in the same memory (see
case of consecutive read cycles in the same memory (see
Figure 26-6. No Setup, No Hold on NRD and NCS Read Signals
26.8.1.5 Null Pulse
Programming null pulse is not permitted. Pulse must be at least set to 1. A null value leads to unpredictable behavior.
26.8.2 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.
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.
26.8.2.1 Read is Controlled by NRD (READ_MODE = 1):
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.
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.
MCK
NRD_PULSE
NCS_RD_PULSE
NRD_CYCLE
NRD_PULSE
NRD_PULSE
NCS_RD_PULSE
NCS_RD_PULSE
NRD_CYCLE
NRD_CYCLE
A[23:0]
NCS
NRD
D[7:0]