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ESMT M12L64164A
Elite Semiconductor Memory Technology Inc. Publication Date: Mar. 2003
Revision: 1.7 11/44
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 V
IL and VIH. During operation with CKE
high all inputs are assumed to be in valid state (low or high)
for the duration of setup and hold time around positive edge
of the clock for proper functionality 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 same as other inputs), the internal clock suspended
from 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 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 synchronous 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.
BANK ADDRESSES (A13~A12)
This SDRAM is organized as four independent banks of
1,048,576 words x 16 bits memory arrays. The A13~A12
inputs are latched at the time of assertion of
RAS and
CAS to select the bank to be used for the operation. The
banks addressed A13~A12 are latched at bank active, read,
write, mode register set and precharge operations.
ADDRESS INPUTS (A0~A11)
The 20 address bits are required to decode the 1,048,576
word locations are multiplexed into 12 address input pins
(A0~A11). The 12 row addresses are latched along with
RAS and A13~A12 during bank active command. The 8 bit
column addresses are latched along with
CAS , WE and
A13~A12 during read or with command.
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.
POWER-UP
1.Apply power and start clock, Attempt to maintain CKE
= “H”, DQM = “H” and the other pins are NOP
condition at the inputs.
2.Maintain stable power, stable clock and NOP input
condition for minimum of 200us.
3.Issue precharge commands for both banks of the
devices.
4.Issue 2 or more auto-refresh commands.
5.Issue a mode register set command to initialize the
mode register.
cf.) Sequence of 4 & 5 is regardless of the order.
The device is now ready for normal operation.
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~A11
and A13~A12 in the same cycle as
CS , RAS , CAS
and
WE going low is the data written in the mode
register. 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 into depending on functionality. 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~A11 and A13~A12. The write burst length is
programmed using A9. A7~A8, A10/AP~A11 and
A13~A12 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.
DVD47 harman/kardon
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