MT48LC4M8A1TG-10 View Datasheet(PDF) - Micron Technology

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MT48LC4M8A1TG-10

SYNCHRONOUS DRAM

Micron Technology 

AUTO REFRESH

AUTO REFRESH is used during normal operation of

the SDRAM and is analagous to CAS#-BEFORE-RAS#

(CBR) REFRESH in conventional DRAMs. This command

is nonpersistent, so it must be issued each time a refresh

is required.

The addressing is generated by the internal refresh

controller. This makes the address bits “Don’t Care”

during an AUTO REFRESH command. The Micron 16Mb

SDRAM requires all of its 4,096 rows to be refreshed every

64ms (tREF). Providing a distributed AUTO REFRESH

command every 15.6µs will meet the refresh require-

ment and ensure that each row is refreshed. Alterna-

tively, all 4,096 AUTO REFRESH commands can be is-

sued in a burst at the minimum cycle rate (tRC) once

every 64ms.

SELF REFRESH

The SELF REFRESH command can be used to re-

tain data in the SDRAM, even if the rest of the system is

powered down. When in the self refresh mode, the SDRAM

retains data without external clocking. The SELF RE-

16 MEG: x4, x8

SDRAM

FRESH command is initiated like an AUTO REFRESH

command except CKE is disabled (LOW). Once the SELF

REFRESH command is registered, all the inputs to the

SDRAM become “Don’t Care,” with the exception of

CKE, which must remain LOW.

Once self refresh mode is engaged, the SDRAM pro-

vides its own internal clocking, causing it to perform its

own AUTO REFRESH cycles. The SDRAM must remain in

self refresh mode for a minimum period equal to tRAS

and may remain in self refresh mode for an indefinite

period beyond that.

The procedure for exiting self refresh requires a se-

quence of commands. First, CLK must be stable prior to

CKE going back HIGH. Once CKE is HIGH, the SDRAM

must have NOP commands issued (a minimum of two

clocks) for tXSR because time is required for the comple-

tion of any internal refresh in progress.

A burst of 4,096 AUTO REFRESH cycles should be

completed just prior to entering and just after exiting the

self refresh mode.

16 Meg: x4, x8 SDRAM

16MSDRAMx4x8_B.p65 – Rev. 5/98

12

Micron Technology, Inc., reserves the right to change products or specifications without notice.

©1998, Micron Technology, Inc.

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