DDR2/mDDR
memory
controller
registers
Hard
Reset from
PLLC0
State
machine
mod_g_rst_n
DDR
PSC
chip_rst_n
Architecture
391
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
DDR2/mDDR Memory Controller
After exiting from the power-down state, the DDR2/mDDR memory controller will drive DDR_CKE high
and then not immediately start executing commands. Instead, it will wait T_XP + 1 clock cycles before
issuing commands. The SDRAM timing register 2 (SDTIMR2) programs the values of T_XP.
See
for a description of the power-down mode programming sequence.
NOTE:
Power-down mode is best suited as a power savings mode when SDRAM is being used
intermittently and the system requires power savings as well as a short recovery time. You
may use self-refresh mode if you desire additional power savings from disabling clocks.
14.2.11 Reset Considerations
The DDR2/mDDR memory controller has two reset signals, chip_rst_n and mod_g_rst_n. The chip_rst_n
is a module-level reset that resets both the state machine as well as the DDR2/mDDR memory controller
memory-mapped registers. The mod_g_rst_n resets the state machine only; it does not reset the
controller's registers, which allows soft reset (from PSC or WDT) to reset the module without resetting the
configuration registers and reduces the programming overhead for setting up access to the DDR2/mDDR
device. If the DDR2/mDDR memory controller is reset independently of other peripherals, the user's
software should not perform memory, as well as register accesses, while chip_rst_n or mod_g_rst_n are
asserted. If memory or register accesses are performed while the DDR2/mDDR memory controller is in
the reset state, other masters may hang. Following the rising edge of chip_rst_n or mod_g_rst_n, the
DDR2/mDDR memory controller immediately begins its initialization sequence. Command and data stored
in the DDR2/mDDR memory controller FIFOs are lost.
describes the different methods for
asserting each reset signal. The Power and Sleep Controller (PSC) acts as a master controller for power
management for all of the peripherals on the device. For detailed information on power management
procedures using the PSC, see the
Power and Sleep Controller (PSC)
chapter.
shows the
DDR2/mDDR memory controller reset diagram.
Table 14-10. Reset Sources
Reset Signal
Reset Source
chip_rst_n
Hardware/device reset
mod_g_rst_n
Power and sleep controller
Figure 14-16. DDR2/mDDR Memory Controller Reset Block Diagram