Architecture
390
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
DDR2/mDDR Memory Controller
In the case of mDDR, after exiting from the self-refresh state, the memory controller will not immediately
start executing commands. Instead, it will wait 1 clock cycles and then execute auto-refresh
command before issuing any other commands. The SDRAM timing register 2 (SDTIMR2) programs the
value of T_SXNR.
Once in self-refresh mode, the DDR2/mDDR memory controller input clocks (VCLK and 2X_CLK) may be
gated off or changed in frequency. Stable clocks must be present before exiting self-refresh mode. See
for more information describing the proper procedure to follow when shutting down
DDR2/mDDR memory controller input clocks.
See
for a description of the self-refresh programming sequence.
14.2.9 Partial Array Self Refresh for Mobile DDR
For additional power savings during self-refresh, the partial array self-refresh (PASR) feature of the mDDR
allows you to select the amount of memory that will be refreshed during self-refresh. Use the partial array
self-refresh (PASR) bit field in the SDRAM configuration register 2 (SDCR2) to select the amount of
memory to refresh during self-refresh. As shown in
you may select either 4, 2, 1, 1/2, or 1/4
bank(s). The PASR bits are loaded into the extended mode register of the mDDR device, during
autoinitialization (see
).
The mDDR performs bank interleaving when the internal bank position (IBANKPOS) bit in SDRAM
configuration register (SDCR) is cleared to 0. Since the SDRAM banks are only partially refreshed during
partial array self-refresh, it is recommended that you set IBANKPOS to 1 to avoid bank interleaving. When
IBANKPOS is cleared to 0, it is the responsibility of software to move critical data into the banks that are
to be refreshed during partial array self-refresh. Refer to
for more information on
IBANKPOS and addressing mapping in general.
Table 14-9. Configuration Bit Field for Partial Array Self-refresh
Bit Field
Bit Value
Bit Description
PASR
Partial array self refresh.
0
Refresh banks 0, 1, 2, and 3
1h
Refresh banks 0 and 1
2h
Refresh bank 0
5h
Refresh 1/2 of bank 0
6h
Refresh 1/4 of bank 0
14.2.10 Power-Down Mode
Setting the self-refresh/low power (SR_PD) bit and the low-power mode enable (LPMODEN) bit in the
SDRAM refresh control register (SDRCR) to 1, forces the DDR2/mDDR memory controller to place the
external DDR2 SDRAM in the power-down mode. When the LPMODEN bit is asserted, the DDR2/mDDR
memory controller continues normal operation until all outstanding memory access requests have been
serviced and the refresh backlog has been cleared. At this point, all open pages of DDR2 SDRAM are
closed and a Power Down command (same as NOP command but driving DDR_CKE low on the same
cycle) is issued.
The DDR2/mDDR memory controller exits the power-down state when a memory access is received,
when a Refresh Must level is reached, when the LPMODEN bit in SDRCR is cleared to 0, or when the
SR_PD bit in SDRCR changed to 0. While in the power-down state, if a request for a memory access is
received, the DDR2/mDDR memory controller services the memory access request, returning to the
power-down state upon completion. The DDR2/mDDR memory controller will not wake-up from the power-
down state (whether from a memory access request, from reaching a Refresh Must level, from clearing
the LPMODEN bit, or from clearing the SR_PD bit) until T_CKE + 1 cycles have expired since the power-
down command was issued. The value of T_CKE is defined in the SDRAM timing register 2 (SDTIMR2).