MB81N643289 Datasheet, PDF (22/64 Pages) Fujitsu Component Limited. – 8 x 256K x 32 BIT DOUBLE DATA RATE FCRAMTM

MB81N643289-50/-60 Preliminary (AE1E)
s FUNCTIONAL DESCRIPTION (continued)
PAGE CLOSE AND PAGE CLOSE OPTION (PC, PCA)
The DDR FCRAM memory core is the same as conventional DRAMs’, requiring Page close and refresh operations.
Page close rewrites the bit line and to reset the internal Row address line and is executed by the Page close operation
(PC or PCA). With the Page close operation, DDR SDRAM will automatically be in standby state after specified
precharge time (tPCL).
The Page closed bank is selected by combination of AC and bank address (BA) when Page close command is
issued. If AC = High, all banks are Page closed regardless of BA (PCA command). If AC = Low, a bank to be selected
by BA is Page closed (PC command).
The auto-pageclose enters Page close mode at the end of burst mode of read or write without Page close command
issue. This auto-pageclose is entered by AC = High when a Read (RD) or Write (WR) command is issued.
Refer to FUNCTION TRUTH TABLE.
AUTO-REFRESH (REF)
Auto-refresh uses the internal refresh address counter. The MB81N643289 Auto-refresh command (REF) automat-
ically generates Bank Active and Page close command internally. All banks of SDRAM should be Page closed prior
to the Auto-refresh command. The Auto-refresh command should also be issued within every 8 µs period.
SELF-REFRESH ENTRY (SELF)
Self-refresh function provides automatic refresh by an internal timer as well as Auto-refresh and will continue the
refresh operation until cancelled by SELFX.
The Self-refresh mode is entered by applying an Auto-refresh command in conjunction with PD = Low (SELF). Once
MB81N643289 enters the self-refresh mode, all inputs except for PD can be either logic high or low level state and
outputs will be in a High-Z state. During Self-refresh mode, PD = Low should be maintained. SELF command should
only be issued after last read data has been appeared on DQ.
Note:
When the burst refresh method is used, a total of 4096 auto-refresh commands within 4 ms must be
asserted prior to the self-refresh mode entry.
SELF-REFRESH EXIT (SELFX)
To exit Self-refresh mode, PD must bring to High for at least 2 clock cycles together with NOP condition.
Refer to Timing Diagram for the detail procedure. It is recommended to issue at least one Auto-refresh command
just after the tRC period to avoid the violation of refresh period.
WARNING:A stable clock for lLOCK period with a constant duty cycle must be supplied prior to applying any command
to insure the DLL is locked against the latest device conditions.
Note:
When the burst refresh method is used, a total of 4096 auto-refresh commands within 4 ms must be
asserted both before the self-refresh entry and after the self-refresh exit.
22