2Gb: x4, x8, x16 DDR3 SDRAM - Micron

Input Clock Frequency Change
2Gb: x4, x8, x16 DDR3 SDRAM
Input Clock Frequency Change
When the DDR3 SDRAM is initialized, the clock must be stable during most normal
states of operation. This means that after the clock frequency has been set to the stable
state, the clock period is not allowed to deviate, except for what is allowed by the clock
jitter and spread spectrum clocking (SSC) specifications.
The input clock frequency can be changed from one stable clock rate to another under
two conditions: self refresh mode and precharge power-down mode. It is illegal to
change the clock frequency outside of those two modes. For the self refresh mode condition,
when the DDR3 SDRAM has been successfully placed into self refresh mode and
tCKSRE has been satisfied, the state of the clock becomes a “Don’t Care.” When the
clock becomes a “Don’t Care,” changing the clock frequency is permissible if the new
clock frequency is stable prior to tCKSRX. When entering and exiting self refresh mode
for the sole purpose of changing the clock frequency, the self refresh entry and exit
specifications must still be met.
The precharge power-down mode condition is when the DDR3 SDRAM is in precharge
power-down mode (either fast exit mode or slow exit mode). Either ODT must be at a
logic LOW or RTT,nom and RTT(WR) must be disabled via MR1 and MR2. This ensures
RTT,nom and RTT(WR) are in an off state prior to entering precharge power-down mode,
and CKE must be at a logic LOW. A minimum of tCKSRE must occur after CKE goes LOW
before the clock frequency can change. The DDR3 SDRAM input clock frequency is allowed
to change only within the minimum and maximum operating frequency specified
for the particular speed grade ( tCK [AVG] MIN to tCK [AVG] MAX). During the input
clock frequency change, CKE must be held at a stable LOW level. When the input clock
frequency is changed, a stable clock must be provided to the DRAM tCKSRX before precharge
power-down may be exited. After precharge power-down is exited and tXP has
been satisfied, the DLL must be reset via the MRS. Depending on the new clock frequency,
additional MRS commands may need to be issued. During the DLL lock time,
RTT,nom and RTT(WR) must remain in an off state. After the DLL lock time, the DRAM is
ready to operate with a new clock frequency.
PDF: 09005aef826aaadc
2Gb_DDR3_SDRAM.pdf – Rev. P 2/12 EN 125 Micron Technology, Inc. reserves the right to change products or specifications without notice.
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