AS4SD4M16(2001) 查看數據表（PDF） - Austin Semiconductor

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AS4SD4M16
(Rev.:2001)

4 Meg x 16 SDRAM Synchronous DRAM Memory

Austin Semiconductor 

Austin Semiconductor, Inc.

SDRAM

AS4SD4M16

BURST TERMINATE

The BURST TERMINATE command is used to trun-

cate either fixed-length or full-page bursts. The most recently

registered READ or WRITE command prior to the BURST TER-

MINATE command will be truncated, as shown in the Opera-

tion section of this data sheet.

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 non-

persistent, 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 64Mb SDRAM requires 4,096

AUTO REFRESH cycles every 64ms *(tREF), regardless of width

option. Providing a distributed AUTO REFRESH command

every 15.625µs/3.906µs will meet the refresh requirement and

ensure that each row is refreshed. Alternatively, 4,096 AUTO

REFRESH commands can be issued in a burst at the minimum

cycle rate (tRC), once every 64ms/ 16ms.

SELF REFRESH

(Industrial -40°C to +85°C Only)

The SELF REFRESH command can be used to retain

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 REFRESH 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

provides 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

sequence 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 completion of any internal

refresh in progress.

If during normal operation AUTO REFRESH cycles

are issued in bursts (as opposed to being evenly distributed),

a burst of 4,096 AUTO REFRESH cycles should be completed

just prior to entering and just after exiting the self refresh mode.

The self refresh option is not available for the -55° to

+125° screening option.

*64ms for -40° to +85° C ( Industrial Temperatures) and 16ms for -55° to +125°C (Military Temperatures)

AS4SD4M16

Rev. 1.5 10/01

11

Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.

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