Texas Instruments OMAP5912 Reference Manual page 140

Traffic Controller
Table 4. Command List (Continued)
Command
Deep power down exit
Deep power down
X = Don't Care
3.3.7 SDRAM Interface ac Parameters
Table 5. ac Parameters Description
82 OMAP3.2 Subsystem
CS RAS CAS
H X X
The difference between power down and deep power down mode is that in case
of power down mode whenever there is an access request to EMIFF, the memory
is brought out of power down by pulling CKE high, but in case of deep power down
mode even when there is an access request the memory is not brought out of deep
power down mode (CKE is still low). The I/O buffers of the memory are deactivated
and although further commands (after having entered deep power down mode) are
accepted by the memory, it does not send or receive any data.
After exit from deep power down mode NOP must be maintained for 200 µs. This
must be followed by PRECHARGE ALLPrecharge all command, followed by eight
autorefreshes, followed by MRS and EMRS commands.
The 2-bit SDRAM frequency (SDF) field in the EMIFF configuration register
allows for selection of a set of ac timings parameters for the interface,
depending on the type and speed grade of the memory component used.
These parameters are commonly used in the SDRAM literature. As the
naming can change from one memory manufacturer to another, the next table
provides the functional description of each individual parameter, as named in
this specification document.
tRC Active to active command period
tRAS Active to precharge command period
tRP Precharge command period
tRCD Active to write/read delay
tRRD Active bank a to active bank b command
Four ac configurations are provided for standard SDR memory components,
and another set of four configurations is provided for the mobile DDR memory.
The selection between these two sets is done automatically, based on the
memory type programmed in the EMIFF operation register.
All parameters are individually specified in number of clock cycles, whereas
in the memory data sheets, absolute values are used for timing parameters.
For a given working frequency, any ac parameter of the selected configuration,
once converted into an absolute timing value, must be greater than the
equivalent parameter specified by the memory manufacturer.
WE CKE ADDR
L → H X
X
SPRU749A