A43E06161
1. Power must be applied to either CKE and DQM inputs to
pull them high and other pins are NOP condition at the
inputs before or along with VDD (and VDDQ) supply.
The clock signal must also be asserted at the same time.
2. After VDD reaches the desired voltage, a minimum pause
of 200 microseconds is required with inputs in NOP
condition.
3. Both banks must be precharged now.
4. Perform a minimum of 2 Auto refresh cycles to stabilize the
internal circuitry.
Device Operations
Clock (CLK)
The clock input is used as the reference for all SDRAM
operations. 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 valid state (low or high)
for the duration of set up and hold time around positive edge
of the clock for proper functionality and ICC specifications.
5. Perform a MODE REGISTER SET cycle to program the
CAS latency, burst length and burst type as the default
value of mode register is undefined.
Clock Enable (CLK)
The clock enable (CKE) gates the clock onto SDRAM. If CKE
goes low synchronously with clock (set-up and hold time
same as other inputs), the internal clock is suspended form
the next clock cycle and the state of output and burst address
is frozen as long as the CKE remains low. All other inputs are
ignored from the next clock cycle after CKE goes low. When
both banks are in the idle state and CKE goes low
synchronously with clock, the SDRAM enters the power down
mode form 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 synchronous as the
internal clock is suspended. When CKE goes high at least
“tSS + 1 CLOCK” before the high going edge of the clock, then
the SDRAM becomes active from the same clock edge
accepting all the input commands.
At the end of one clock cycle from the mode register set
cycle, the device is ready for operation.
When the above sequence is used for Power-up, all the
out-puts will be in high impedance state. The high
impedance of outputs is not guaranteed in any other
power-up sequence.
cf.) Sequence of 4 & 5 may be changed.
Mode Register Set (MRS)
The mode register stores the data for controlling the various
operation modes of SDRAM. It programs the CAS latency,
addressing mode, 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
Bank Select (BA)
written by asserting low on
SDRAM should be in active mode with CKE already high
prior to writing the mode register). The state of address pins
,
,
,
(The
WE
CS RAS CAS
This SDRAM is organized as two independent banks of
524,288 words X 16 bits memory arrays. The BA inputs is
latched at the time of assertion of
and
to select
CAS
RAS
A0~A10/AP
and
BA
in
the
same
cycle
as
the bank to be used for the operation. When BA is asserted
low, bank A is selected. When BA is asserted high, bank B is
selected. The bank select BA is latched at bank activate,
read, write mode register set and precharge operations.
,
,
,
going low is the data written in the
WE
CS RAS CAS
mode register. One clock cycle 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 both banks are in
the idle state. The mode register is divided into various fields
depending on functionality. The burst length field uses
A0~A2, burst type uses A3, addressing mode uses A4~A6,
A7~A8, A10/AP and BA are used for vendor specific options
or test mode. And the write burst length is programmed using
A9. A7~A8, A10/AP and BA must be set to low for normal
SDRAM operation.
Address Input (A0 ~ A10/AP)
The 19 address bits required to decode the 524,288 word
locations are multiplexed into 11 address input pins
(A0~A10/AP). The 11 bit row address is latched along with
and BA during bank activate command. The 8 bit
RAS
column address is latched along with
,
and BA
WE
CAS
during read or write command.
Refer to table for specific codes for various burst length,
addressing modes and CAS latencies.
NOP and Device Deselect
Bank Activate
When
,
and
are high, the SDRAM performs
WE
RAS CAS
The bank activate command is used to select a random row
no operation (NOP). NOP does not initiate any new
operation, but is needed to complete operations which
require more than single clock like bank activate, burst read,
auto refresh, etc. The device deselect is also a NOP and is
in an idle bank. By asserting low on
and
with
CS
RAS
desired row and bank addresses, a row access is initiated.
The read or write operation can occur after a time delay of
tRCD(min) from the time of bank activation. tRCD(min) is an
internal timing parameter of SDRAM, therefore it is
dependent on operating clock frequency. The minimum
number of clock cycles required between bank activate and
read or write command should be calculated by dividing
tRCD(min) with cycle time of the clock and then rounding off
the result to the next higher integer. The SDRAM has two
internal banks on the same chip and shares part of the
internal circuitry to reduce chip area, therefore it restricts the
entered by asserting
high.
high disables the
CS
CS
command decoder so that
address inputs are ignored.
,
and , and all the
WE
RAS CAS
Power-Up
The following sequence is recommended for POWER UP
PRELIMINARY (July, 2005, Version 0.1)
11
AMIC Technology, Corp.
AMICC [ AMIC TECHNOLOGY ]
