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Architecture
846
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
External Memory Interface A (EMIFA)
19.2.4.8 Power Down Mode
To support low-power modes, the EMIFA can be requested to issue a POWER DOWN command to the
SDRAM by setting the PD bit in the SDRAM configuration register (SDCR). When this bit is set, the
EMIFA will continue normal operation until all outstanding memory access requests have been serviced
and the SDRAM refresh backlog (if there is one) has been cleared. At this point the EMIFA will enter the
power-down state. Upon entering this state, the EMIFA will issue a POWER DOWN command (same as a
NOP command but driving EMA_SDCKE low on the same cycle). The EMIFA then maintains
EMA_SDCKE low until it exits the power-down state.
Since the EMIFA services the refresh backlog before it enters the power-down state, all internal banks of
the SDRAM are closed (precharged) prior to issuing the POWER DOWN command. Therefore, the EMIFA
only supports Precharge Power Down. The EMIFA does not support Active Power Down, where internal
banks of the SDRAM are open (active) before the POWER DOWN command is issued.
During the power-down state, the EMIFA services the SDRAM, asynchronous memory, and register
accesses as normal, returning to the power-down state upon completion.
The PDWR bit in SDCR indicates whether the EMIFA should perform refreshes in power-down state. If the
PDWR bit is set, the EMIFA exits the power-down state every time the Refresh Must level is set, performs
AUTO REFRESH commands to the SDRAM, and returns back to the power-down state. This evenly
distributes the refreshes to the SDRAM in power-down state. If the PDWR bit is not set, the EMIFA does
not perform any refreshes to the SDRAM. Therefore, the data integrity of the SDRAM is not assured upon
power down exit if the PDWR bit is not set.
If the PD bit is cleared while in the power-down state, the EMIFA will come out of the power-down state.
The EMIFA:
•
Drives EMA_SDCKE high.
•
Enters its idle state.