K5D5657DCM-F015 Datasheet, PDF (42/74 Pages) Samsung semiconductor – MCP Specification of 256Mb NAND and 256Mb Mobile SDRAM

K5D5657DCM-F015
Preliminary
MCP MEMORY
D. DEVICE OPERATIONS (continued)
CLOCK (CLK)
The clock input is used as the reference for all SDRAM opera-
tions. All operations are synchronized to the positive going edge
of the clock. The clock transitions must be monotonic between
VIL and VIH. During operation with CKE high all inputs are
assumed to be in a valid state (low or high) for the duration of
set-up and hold time around positive edge of the clock in order to
function well Q perform and ICC specifications.
CLOCK ENABLE (CKE)
The clock enable(CKE) gates the clock onto SDRAM. If CKE
goes low synchronously with clock (set-up and hold time are the
same as other inputs), the internal clock is suspended from the
next clock cycle and the state of output and burst address is fro-
zen as long as the CKE remains low. All other inputs are ignored
from the next clock cycle after CKE goes low. When all banks are
in the idle state and CKE goes low synchronously with clock, the
SDRAM enters the power down mode from the next clock cycle.
The SDRAM remains in the power down mode ignoring the other
inputs as long as CKE remains low. The power down exit is syn-
chronous as the internal clock is suspended. When CKE goes
high at least "1CLK + tSS" before the high going edge of the
clock, then the SDRAM becomes active from the same clock
edge accepting all the input commands.
NOP and DEVICE DESELECT
When RAS, CAS and WE are high, the SDRAM performs no
operation (NOP). NOP does not initiate any new operation, but is
needed to complete operations which require more than single
clock cycle like bank activate, burst read, auto refresh, etc. The
device deselect is also a NOP and is entered by asserting CS
high. CS high disables the command decoder so that RAS, CAS,
WE and all the address inputs are ignored.
DQM OPERATION
The DQM is used to mask input and output operations. It works
similar to OE during read operation and inhibits writing during
write operation. The read latency is two cycles from DQM and
zero cycle for write, which means DQM masking occurs two
cycles later in read cycle and occurs in the same cycle during
write cycle. DQM operation is synchronous with the clock. The
DQM signal is important during burst interruptions of write with
read or precharge in the SDRAM. Due to asynchronous nature of
the internal write, the DQM operation is critical to avoid unwanted
or incomplete writes when the complete burst write is not
required. Please refer to DQM timing diagram also.
MODE REGISTER SET (MRS)
The mode register stores the data for controlling the various
operating modes of SDRAM. It programs the CAS latency, burst
type, burst length, test mode and various vendor specific options
to make SDRAM useful for variety of different applications. The
default value of the mode register is not defined, therefore the
mode register must be written after power up to operate the
SDRAM. The mode register is written by asserting low on CS,
RAS, CAS and WE (The SDRAM should be in active mode with
CKE already high prior to writing the mode register). The state of
address pins A0 ~ An and BA0 ~ BA1 in the same cycle as CS,
RAS, CAS and WE going low is the data written in the mode reg-
ister. Two clock cycles is required to complete the write in the
mode register. The mode register contents can be changed
using the same command and clock cycle requirements during
operation as long as all banks are in the idle state. The mode
register is divided into various fields depending on the fields of
functions. The burst length field uses A0 ~ A2, burst type uses
A3, CAS latency (read latency from column address) use A4 ~
A6, vendor specific options or test mode use A7 ~ A8, A10/AP ~
An and BA0 ~ BA1. The write burst length is programmed using
A9. A7 ~ A8, A10/AP ~ An and BA0 ~ BA1 must be set to low for
normal SDRAM operation. Refer to the table for specific codes
for various burst length, burst type and CAS latencies.
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Revision 0.0
June 2003