HY5S5B2BLF-6E Datasheet, PDF (42/54 Pages) Hynix Semiconductor – 256M (8Mx32bit) Mobile SDRAM

11
256Mbit (8Mx32bit) Mobile SDR Memory
HY5S5B2BLF(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
AUTO REFRESH commands at an average periodic interval of tREF.
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
8*tREF.
-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
value of PASR(Partial Array Self Refresh). The Mobile SDRAM can reduce the self refresh current(IDD6) by using these
two modes.
Rev 1.0 / Apr. 2006
42