V55C2128164V datasheet(6/44 Pages) MOSEL

Part #	V55C2128164V

Description	128Mbit LOW-POWER SDRAM 2.5 VOLT, TSOP II / BGA PACKAGE 8M X 16

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Manufacturer	MOSEL [Mosel Vitelic, Corp]

Direct Link	http://www.moselvitelic.com

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V55C2128164V(T/B) Rev.1.2 August 2002

MOSEL VITELIC

V55C2128164V(T/B)

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 and Low Power Mode Register Set

Command must be issued to initialize the Mode

Register. A minimum of two 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.

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

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.

Low Power Mode Register

The Low Power Mode Register controls functions

beyond those controlled by the Mode Register.

These additional functions are unique to the Low-

Power DRM and includes a Refresh Period field

(TCR) for temperature compensated self-refresh

and a Partial-Array Self-Refresh field (PAS). The

PASR field is used to specify whether only one

quarter (bank 0), one half (bank 0+1) or all banks of

the SDRAM array are enabled. Disabled banks will

not be refreshed in Self-Refresh mode and written

data will be lost. When only bank 0 is selected, it’s

possible to partially select only half or mone quarter

of bank 0. The TCR field has four entries to set Re-

fresh Period during self-refresh depending on the

case temperature of the Low power RAM. It’s re-

quired during the initialization seuqence and can be

modified when the part id idle.

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, tRCD, from the

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.

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