Rev 1.0 / Jan. 2007

39

11

512Mbit (32Mx16bit) Mobile SDR Memory

HY5S7B6LF(P) Series

AUTO REFRESH AND SELF REFRESH

Mobile SDRAM devices require a refresh of all rows in any rolling 64ms interval. Each refresh is generated in one of two

ways: by an explicit AUTO REFRESH command, or by an internally timed event in SELF REFRESH mode:

-

AUTO REFRESH.

This command is used during normal operation of the Mobile SDRAM. It is non persistent, so must be issued each time

a refresh is required. The refresh addressing is generated by the internal refresh controller.The Mobile SDRAM requires

To allow for improved efficiency in scheduling and switching between tasks, some flexibility in the absolute refresh

interval is provided. A maximum of eight AUTO REFRESH commands can be posted to any given Mobile SDRMA, and

the maximum absolute interval between any AUTO REFRESH command and the next AUTO REFRESH command is

-SELF REFRESH.

This state retains data in the Mobile SDRAM, even if the rest of the system is powered down. Note refresh interval tim-

ing while in Self Refresh mode is scheduled internally in the Mobile SDRAM and may vary and may not meet tREF time.

After executing a self-refresh command, the self-refresh operation continues while CKE is held Low. During selfrefresh

operation, all ROW addresses are refreshed by the internal refresh timer. A self-refresh is terminated by a self-refresh

exit command. Before and after self-refresh mode, execute auto-refresh to all refresh addresses in or within tREF

(max.) period on the condition 1 and 2 below.

1. Enter self-refresh mode within time as below* after either burst refresh or distributed refresh at equal interval to all

refresh addresses are completed.

2. Start burst refresh or distributed refresh at equal interval to all refresh addresses within time as below*after exiting

from self-refresh mode.

Note: tREF (max.) / refresh cycles.

The use of SELF REFRESH mode introduces the possibility that an internally timed event can be missed when CKE is

raised for exit from self refresh mode. Upon exit from SELF REFRESH an extra AUTO REFRESH command is recom-

mended. In the self refresh mode, two additional power-saving options exist. They are Temperature Compensated Self

Refresh and Partial Array Self Refresh and are described in the Extended Mode Register section.

The Self Refresh command is used to retain cell data in the Mobile SDRAM. In the Self Refresh mode, the Mobile

SDRAM operates refresh cycle asynchronously.

The Self Refresh command is initiated like an Auto Refresh command except CKE is disabled(Low). The Mobile SDRAM

can accomplish an special Self Refresh operation by the specific modes(PASR) programmed in extended mode regis-

ters. The Mobile SDRAM can control the refresh rate automatically by the temperature value of Auto TCSR(Tempera-

ture Compensated Self Refresh) to reduce self refresh current and select the memory array to be refreshed by the

two modes.