Datasheet

SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
448
25.15 Slow Clock Mode
The SMC is able to automatically apply a set of “slow clock mode” read/write waveforms when an internal signal
driven by the Power Management Controller is asserted because MCK has been turned to a very slow clock rate
(typically 32 kHz clock rate). In this mode, the user-programmed waveforms are ignored and the slow clock mode
waveforms are applied. This mode is provided so as to avoid reprogramming the User Interface with appropriate
waveforms at very slow clock rate. When activated, the slow mode is active on all chip selects.
25.15.1 Slow Clock Mode Waveforms
Figure 25-28 illustrates the read and write operations in slow clock mode. They are valid on all chip selects. Table
25-8 indicates the value of read and write parameters in slow clock mode.
Figure 25-28. Read/Write Cycles in Slow Clock Mode
25.15.2 Switching from (to) Slow Clock Mode to (from) Normal Mode
When switching from slow clock mode to normal mode, the current slow clock mode transfer is completed at high
clock rate, with the set of slow clock mode parameters. See Figure 25-29. The external device may not be fast
enough to support such timings.
Figure 25-30 illustrates the recommended procedure to properly switch from one mode to the other.
A[ 23:2]
NCS
1
MCK
NWE 1
1
NWE_CYCLE = 3
A [23:2]
MCK
NRD
NRD_CYCLE = 2
1
1
NCS
SLOW CLOCK MODE WRITE SLOW CLOCK MODE READ
NBS0, NBS1,
A0,A1
NBS0, NBS1,
A0,A1
Table 25-8. Read and Write Timing Parameters in Slow Clock Mode
Read Parameters Duration (cycles) Write Parameters Duration (cycles)
NRD_SETUP 1 NWE_SETUP 1
NRD_PULSE 1 NWE_PULSE 1
NCS_RD_SETUP 0 NCS_WR_SETUP 0
NCS_RD_PULSE 2 NCS_WR_PULSE 3
NRD_CYCLE 2 NWE_CYCLE 3