AS4SD16M16 datasheet(17/52 Pages) MICROSS

17 / 52 page

SDRAM

AS4SD16M16

Rev. 2.6 04/13/15

Micross Components reserves the right to change products or specifications without notice.

Data for any WRITE burst may be truncated with a sub-

sequent READ command, and data for a fixed-length WRITE

burst may be immediately followed by a READ command.

Once the READ command is registered, the data inputs will

ignored, and WRITEs will not be executed. An example

is shown in Figure 17. Data n+1 is either the last of a burst of

two or the last desired of a longer burst.

Data for a fixed-length WRITE burst may be followed by,

or truncated with, a PRECHARGE command to the same bank

(provided that auto precharge was not activated), and a full-page

WRITE burst may be truncated with a PRECHARGE command

to the same bank. The PRECHARGE command should be

issued t

WR after the clock edge at which the last desired input

data element is registered. The auto precharge mode requires

a t

WR of at least one clock plus time, regardless of frequency.

In addition, when truncating a WRITE burst, the DQM signal

must be used to mask input data for the clock edge prior to, and

the clock edge coincident with, the PRECHARGE command.

An example is shown in Figure 18. Data n+1 is either the last

of a burst of two or the last desired of a longer burst. Following

the PRECHARGE command, a subsequent command to the

same bank cannot be issued until tRP is met. The precharge

can be issued coincident with the first coincident clock edge

(T2 in Figure 18) on an A1 Version and with the second clock

on an A2 Version (Figure 18).

In the case of a fixed-length burst being executed to com-

pletion, a PRECHARGE command issued at the optimum time

(as described above) provides the same operation that would

result from the same fixed-length burst with auto precharge.

The disadvantage of the PRECHARGE command is that is

requires that the command and address buses be available at

the appropriate time to issue the command; the advantage of

the PRECHARGE command is that it can be used to truncate

fixed-length or full-page bursts.

FIGURE 16: Random WRITE Cycles

FIGURE 17: WRITE to READ

FIGURE 18: WRITE to PRECHARGE

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