M32L1632512A
DEVICE OPERATIONS (Continued)
The minimum number of clock cycles required to
complete row precharge is calculated by dividing
“tRP” with clock cycle time and rounding up to the
next higher integer. Care should be taken to make
sure that burst write is completed or DQM is used
to inhibit writing before precharge command is
asserted. The maximum time any bank can be
active is specified by tRAS (max). Therefore, each
bank has to be precharged within tRAS (max) from
the bank activate command. At the end of
precharge, the bank enters the idle state and is ready
to be activated again.
AUTO REFRESH
The storage cells of SGRAM 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
and
with high on CKE and
WE
.
RAS
CAS
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 them 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 SGRAM is being used
for normal data transactions. The auto refresh
cycle can be performed once in 15.6us or the
burst of 2048 auto refresh cycles in 32ms.
Entry to Power Down, Auto refresh, Self refresh
and Mode register Set etc. is possible only when
both banks are in idle state.
AUTO PRECHARGE
The precharge operation can also be performed by
using auto precharge. The SGRAM 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 A9. If burst read or burst write command is
issued with low on A9, the bank is left active until a
new command is asserted. Once auto precharge
command is given, no new command are possible
to that particular bank until the bank achieves idle
state.
SELF REFRESH
The self refresh is another refresh mode
available in the SGRAM. The self refresh is the
preferred refresh mode for data retention and
low power operation of SGRAM. In self refresh
mode, the SGRAM disables the internal clock
and all the input buffers except CKE. The
refresh addressing and timing is internally
generated to reduce power consumption.
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 A9 after all
banks have satisfied tRAS (min) requirement, performs
precharge on both banks. At the end of tRP after
performing precharge all, all banks are in idle state.
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
Elite Semiconductor Memory Technology Inc.
Publication Date : Jun. 2001
Revision : 1.6
16/54
ESMT [ ELITE SEMICONDUCTOR MEMORY TECHNOLOGY INC. ]
