A43L0616AV datasheet(15/45 Pages) AMICC

15 / 45 page

A43L0616A

(May, 2001, Version 1.0)

AMIC Technology, Inc.

Device Operations (continued)

Auto Precharge

The precharge operation can also be performed by using

auto precharge. The SDRAM internally generates the timing

to satisfy tRAS(min) and “tRP” for the programmed burst length

and CAS latency. The auto precharge command is issued at

the same time as burst read or burst write by asserting high

on A10/AP. If burst read or burst write command is issued

with low on A10/AP, the bank is left active until a new

command is asserted. Once auto precharge command is

given, no new commands are possible to that particular bank

until the bank achieves idle state.

Both Banks Precharge

Both banks can be precharged at the same time by using

Precharge all command. Asserting low on

CS ,

RAS and

WE with high on A10/AP after both banks have satisfied

tRAS(min) requirement, performs precharge on both banks. At

the end of tRP after performing precharge all, both banks

are in idle state.

Auto Refresh

The storage cells of SDRAM need to be refreshed every

32ms to maintain data. An auto refresh cycle accomplishes

refresh of a single row of storage cells. The internal counter

increments automatically on every auto refresh cycle to

refresh all the rows. An auto refresh command is issued by

asserting low on

CS ,

RAS and CAS with high on CKE

and

WE . The auto refresh command can only be asserted

with both banks being in idle state and the device is not in

power down mode (CKE is high in the previous cycle). The

time required to complete the auto refresh

operation is specified by “tRC(min)”. The minimum number of

clock cycles required can be calculated by driving “tRC” with

clock cycle time and then rounding up to the next higher

integer. The auto refresh command must be followed by

NOP’s until the auto refresh operation is completed. Both

banks will be in the idle state at the end of auto refresh

operation. The auto refresh is the preferred refresh mode

when

the

SDRAM

being

used

for

normal

data

transactions. The auto refresh cycle can be performed once

in 15.6us or a burst of 2048 auto refresh cycles once in

32ms.

Self Refresh

The self refresh is another refresh mode available in the

SDRAM. The self refresh is the preferred refresh mode for

data retention and low power operation of SDRAM. In self

refresh mode, the SDRAM disables the internal clock and all

the input buffers except CKE. The refresh addressing and

timing is internally generated to reduce power consumption.

The self refresh mode is entered from all banks idle state by

asserting low on

CS ,

RAS , CAS and CKE with high on

WE . Once the self refresh mode is entered, only CKE state

being low matters, all the other inputs including clock are

ignored to remain in the self refresh.

The self refresh is exited by restarting the external clock and

then asserting high on CKE. This must be followed by NOP’s

for a minimum time of “tRC” before the SDRAM reaches idle

state to begin normal operation. If the system uses burst

auto refresh during normal operation, it is recommended to

used burst 2048 auto refresh cycles immediately after exiting

self refresh.

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