V54C3128(16/80/40)4V(T/S)
operation must be done before any activate com-
mand after the initial power up. Any content of the
mode register can be altered by re-executing the
mode set command. All banks must be in pre-
charged state and CKE must be high at least one
clock before the mode set operation. After the mode
register is set, a Standby or NOP command is re-
quired. Low signals of RAS, CAS, and WE at the
positive edge of the clock activate the mode set op-
eration. Address input data at this timing defines pa-
rameters to be set as shown in the previous table.
Power On and Initialization
The default power on state of the mode register is
supplier specific and may be undefined. The
following power on and initialization sequence
guarantees the device is preconditioned to each
users specific needs. Like a conventional DRAM,
the Synchronous DRAM must be powered up and
initialized in a predefined manner. During power on,
all VCC and VCCQ pins must be built up
simultaneously to the specified voltage when the
input signals are held in the “NOP” state. The power
on voltage must not exceed VCC+0.3V on any of
the input pins or VCC supplies. The CLK signal
must be started at the same time. After power on,
an initial pause of 200 µs is required followed by a
precharge of both banks using the precharge
command. To prevent data contention on the DQ
bus during power on, it is required that the DQM and
CKE pins be held high during the initial pause
period. Once all banks have been precharged, the
Mode Register Set Command must be issued to
initialize the Mode Register. A minimum of eight
Auto Refresh cycles (CBR) are also required.These
may be done before or after programming the Mode
Register. Failure to follow these steps may lead to
unpredictable start-up modes.
Read and Write Operation
When RAS is low and both CAS and WE are high
at the positive edge of the clock, a RAS cycle starts.
According to address data, a word line of the select-
ed bank is activated and all of sense amplifiers as-
sociated to the wordline are set. A CAS cycle is
triggered by setting RAS high and CAS low at a
clock timing after a necessary delay, t
, from the
RCD
RAS timing. WE is used to define either a read
(WE = H) or a write (WE = L) at this stage.
SDRAM provides a wide variety of fast access
modes. In a single CAS cycle, serial data read or
write operations are allowed at up to a 125 MHz
data rate. The numbers of serial data bits are the
burst length programmed at the mode set operation,
i.e., one of 1, 2, 4, 8. Column addresses are seg-
mented by the burst length and serial data accesses
are done within this boundary. The first column ad-
dress to be accessed is supplied at the CAS timing
and the subsequent addresses are generated auto-
matically by the programmed burst length and its
sequence. For example, in a burst length of 8 with
interleave sequence, if the first address is ‘2’, then
the rest of the burst sequence is 3, 0, 1, 6, 7, 4, and
5.
Programming the Mode Register
The Mode register designates the operation
mode at the read or write cycle. This register is di-
vided into 4 fields. A Burst Length Field to set the
length of the burst, an Addressing Selection bit to
program the column access sequence in a burst cy-
cle (interleaved or sequential), a CAS Latency Field
to set the access time at clock cycle and a Opera-
tion mode field to differentiate between normal op-
eration (Burst read and burst Write) and a special
Burst Read and Single Write mode. The mode set
V54C3128(16/80/40)4V(T/S) Rev. 1.2 August 2002
11
MOSEL [ MOSEL VITELIC, CORP ]
