HYB39S164400 Datasheet, PDF (11/64 Pages) Siemens Semiconductor Group – 16 MBit Synchronous DRAM

HYB39S16400/800/160BT-8/-10
16MBit Synchronous DRAM
DQM Function
DQM has two functions for data I/O read write operations. During reads, when it turns to high
at a clock timing, data outputs are disabled and become high impedance after two clock delay (DQM
Data Disable Latency t_DQZ). It also provides a data mask function for writes. When DQM is
activated, the write operation at the next clock is prohibited (DQM Write Mask Latency t _DQW = zero
clocks).
Suspend Mode
During normal access mode, CKE is held high and CLK is enabled. When CKE is low, it freezes
the internal clock and extends data read and write operations. One clock delay is required for mode
entry and exit (Clock Suspend Latency t_CSL).
Power Down
In order to reduce standby power consumption, a power down mode is available. Bringing CKE
low enters the power down mode and all of receiver circuits are gated. All banks must be
precharged before entering this mode. One clock delay is required for mode entry and exit. The
Power Down mode does not perform any refresh operation.
Auto Precharge
Two methods are available to precharge SDRAMs. In an automatic precharge mode, the CAS
timing accepts one extra address, CA10, to determine whether the chip restores or not after the
operation. If CA10 is high when a Read Command is issued, the Read with Auto-Precharge
function is initiated. The SDRAM automatically enters the precharge operation one clock after the
Read Command is registered for CAS latencies of 1 and 2, and two clocks for CAS latencies of 3.
If CAS10 is high when a Write Command is issued, the Write with Auto-Precharge function is
initiated. The SDRAM automatically enters the precharge operation one clock delay form the last
data-in for CAS latencies of 1 and 2 and two clocks for CAS latencies of 3. This delay is referenced
as t_DPL .
Precharge Command
If CA10 is low, the chip needs another way to precharge. In this mode, a separate precharge
command is necessary. When RAS and WE are low and CAS is high at a clock timing, it triggers the
precharge operation. Two address bits, A10 and A11, are used to define banks as shown in the
following list. The precharge command may be applied coincident with the last of burst reads for
CAS Latency = 1 and with the second to the last read data for CAS Latencies = 2 & 3. Writes require
a time t_DPL from the last burst data to apply the precharge command.
Bank Selection by Address Bits
A10
A11
Bank A Only
Low
Low
Bank B Only
Low
High
Both A and B
High
Dont’ Care
Semiconductor Group
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