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引用 (原创)SDRAM 学习笔记<二>

(2010-07-20 14:52:32)
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音乐

预充电

to

and

of

杂谈

WRITE to PRECHARGE 从写切换到预充电

Data for any WRITE burst may be followed by a subsequent PRECHARGE command to the same bank (provided Auto Precharge was not activated). When the precharge command is executed for the same bank as the write command that preceded it, the minimum interval between the two commands is 1 clock.

如果自动预充电无效,那么写指令后可以切换到同bank的预充电指令上。但是两个指令之间需要间隔至少1个时钟周期。

However, if the burst write operation is unfinished, the input data must be masked by means of DQM for assurance of the clock defined by tDPL.

如果写操作尚未完成就需要预充电,那么就需要用DQM信号来对输入数据总线进行屏蔽,以满足规定的tDPL时间。

Data for any WRITE burst may be truncated by a subsequent PRECHARGE command.Note that only data-inthat are registered prior to the tDPL period are written to the internal array, and any subsequent data-in should be masked with DM.

写操作会被预充电指令中断,但是在tDPL时间之前就被锁存的数据会被写入存储器,之后的数据就会被DM信号屏蔽。

Following the PRECHARGE command, a subsequent command to the same bank cannot be issued until tRP is met.

在预充电之后发出的命令,间隔需要满足tRP时间。

 

BURST TERMINATE 访问终止

The BURST TERMINATE command is used to truncate read bursts (with autoprecharge disabled).

BURST TERMINATE指令用于中断读操作。

The most recently registered READ command prior to the BURST TERMINATE command will be truncated.

在BURST TERMINATE指令之前锁存的最后一个读指令会被中断。

Note the BURST TERMINATE command is not bank specific. This command should not be used to terminate write bursts.

BURST TERMINATE指令与bank无关。这个指令不能中断写操作。

 

PRECHARGE 预充电

The PRECHARGE command is used to deactivate the open row in a particular bank or the open row in all banks. Another command to the same bank (or banks) being precharged must not be issued until the precharge time (tRP) is completed.

预充电指令用于将某个或者全部bank上的有效行关闭的指令。其他指令要发送(操作该bank),需要至少等待tRP时间。

If one bank is to be precharged, the particular bank address needs to be specified. If all banks are to be precharged, A10 should be set high along with the PRECHARGE command. If A10 is high, BA0 and BA1 are ignored.

如果对一个bank进行预充电操作,就需要制定BA的值。如果所有的bank进行预充电操作,A10需要在整个预充电指令期间为高。如果A10为高,BA的输入会被忽略。

A PRECHARGE command will be treated as a NOP if there is no open row in that bank, or if the previously open row is already in the process of precharging.

在该bank上没有有效行或者预充电操作已经开始运行,新的预充电操作就会被当做NOP指令。

 

A10的作用:

A10 defines the precharge mode when a precharge command, a read command or a write command is

Issued.

A10在预充电或者读写指令发出时,其决定了预充电的模式;

If A10 = High when a precharge command is issued, all banks are precharged.

If A10 = Low when a precharge command is issued, only the bank that is selected by BA1/BA0 is

Precharged.

在预充电指令发出时,如果A10为高,则所有bank预充电。如果A10为低,则BA所指定的bank预充电。

If A10 = High when read or write command, autoprecharge function is enabled. While A10 = Low, autoprecharge function is disabled.

在读写指令发出时,如果A10为高,则代表开启了自动预充电模式,否则自动预充电无效。

 

AUTO REFRESH AND SELF REFRESH  自动刷新和自刷新

Hynix SDR 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:

SDRAM需要在64ms内刷新一次。刷新通过自动刷新指令和自刷新指令来完成。

- AUTO REFRESH. 自动刷新

This command is used during normal operation of the Hynix SDR 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 Hynix SDR SDRAM requires AUTO REFRESH commands at an average periodic interval of tREF.

这个指令不能连续运行,每次都需要发出一个自动刷新指令。发出自动刷新指令的间隔周期平均为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 SDR SDRAM, and the maximum absolute interval between any AUTO REFRESH command and the next AUTO REFRESH command is 8*tREF。

为了提高时序性能和降低任务切换的复杂度,可以一次给SDRAM发送8个自动刷新指令,从而使得发出自动刷新指令的间隔时间变为8*tREF。

-SELF REFRESH. 自刷新

The Self Refresh command is initiated like an Auto Refresh command except CKE is disabled(Low). This state retains data in the SDR SDRAM, even if the rest of the system is powered down. Note refresh interval timing while in Self Refresh mode is scheduled internally in the SDR SDRAM and may vary and may not meet tREF time.

自刷新指令和自动刷新指令一样,除了CKE信号是无效的。这样可以保持SDRAM中的数据,即便是系统的其他模块处于power down。刷新的时间是芯片内部时序控制的,可变且可以不满足tREF时间。

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.

在执行自刷新指令后,如果CKE信号一直为低,则一直处于自刷新模式,刷新地址由其内部计数器提供。通过自刷新退出指令可以中断自刷新。在开始和结束自刷新前,执行自动刷新。

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 recommended.

CKE升高后,会退出自刷新模式。此时需要外加自动刷新指令。

The Self Refresh command is used to retain cell data in the SDR SDRAM. In the Self Refresh mode, the SDR SDRAM operates refresh cycle asynchronously.

If all banks are in the idle status and CKE is inactive (low level), the self refresh mode is set.

在所有的bank处于IDLE状态时,如果将CKE拉低,则进入自刷新模式。

 

MODE REGISTER SET 模式寄存器设置

The mode registers are loaded via the address bits. BA0 and BA1 are used to select the Mode Register.

通过地址位进入模式寄存器,BA用于选择模式寄存器。BA0=BA1=Low loads the Mode Register。

The MODE REGISTER SET command can only be issued when all banks are idle and no bursts are in progress, and a subsequent executable command cannot be issued until tMRD is met.

模式寄存器指令只能在所有的bank都在idle状态,没有任何访问进行时,才能够发出。发出模式寄存器设置指令后,需要至少过 tMRD才能发出新的指令。

 

POWER DOWN

Power down occurs if CKE is set low coincident with Device Deselect or NOP command and when no accesses are in progress.

在没有访问正在进行时,将CKE拉低,并且此时片选无效或者发出的时NOP指令,那么芯片就会power down。

If power down occurs when all banks are idle, it is Precharge Power Down.

如果所有bank都在idle状态时进入power down状态,这叫Precharge Power Down。

If Power down occurs when one or more banks are Active, it is referred to as Active power down. The device cannot stay in this mode for longer than the refresh requirements of the device, without losing data.

如果有bank还在有效,这样的power down叫做Active power down。这个状态保持不了很久,不能超过设备刷新的间隔,否则设备会丢数据。

The power down state is exited by setting CKE high while issuing a Device Deselect or NOP command.

如果将CKE拉高,同时发出片选无效或者NOP指令,设备会脱离power down状态。

Entering power-down deactivates the input and output buffers, excluding CKE, for maximum power savings while in standby.

进入power-down后,会使输入输出buffer无效,但CKE除外,可以最大限度地降低功耗。

 

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