External Memory Interface Handbook Volume 3: Reference Material

ID 683841
Date 7/24/2019
Document Table of Contents

7.3.6. Low-Power Logic

There are two types of low-power logic: the user-controlled self-refresh logic and automatic power-down with programmable time-out logic.

User-Controlled Self-Refresh

When you assert the local_self_rfsh_req signal, the controller completes any currently executing reads and writes, and then interrupts the command queue and immediately places the memory into self-refresh mode. When the controller places the memory into self-refresh mode, it responds by asserting an acknowledge signal, local_self_rfsh_ack. You can leave the memory in self-refresh mode for as long as you choose.

To bring the memory out of self-refresh mode, you must deassert the request signal, and the controller responds by deasserting the acknowledge signal when the memory is no longer in self-refresh mode.

Note: If a user-controlled refresh request and a system-generated refresh request occur at the same time, the user-controlled refresh takes priority; the system-generated refresh is processed only after the user-controlled refresh request is completed.

Automatic Power-Down with Programmable Time-Out

The controller automatically places the memory in power-down mode to save power if the requested number of idle controller clock cycles is observed in the controller. The Auto Power Down Cycles parameter on the Controller Settings tab allows you to specify a range between 1 to 65,535 idle controller clock cycles. The counter for the programmable time-out starts when there are no user read or write requests in the command queue. Once the controller places the memory in power-down mode, it responds by asserting the acknowledge signal, local_power_down_ack.

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