HYB 39S128400/800/160CT(L)
128-MBit Synchronous DRAM
INFINEON Technologies 11 7.01
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
user s speci fic needs. Like a conve ntional D RAM, t he Synchronous DRAM must be powered up and
initialized in a predefined manner. During power on, all VDD and VDDQ 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 VDD + 0.3 V on any of the input pins or VDD supplies. The CLK
signal must be started at the same time. After power on, an initial pause of 200 µs is required
foll owed by a pr echarge of al l banks us ing t he prechar ge command. To prevent data c ontention on
the DQ bus during power on, it i s required that the DQM and CKE pins be held high during the i nitial
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.
Programming the Mode Register
The Mode registe r designates the operati on mode at the read or write cycle. This regis ter is divi ded
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 cycle (interleaved or sequential), a CAS Latency
Field to set the access time at clock cycle and a Operation mode field to differentiate between
normal operation (Burst read and burst Write) and a special Burst Read and Single Write mode.
After the initi al power up, the mode set operation must be done before any activate command. Any
content o f the mode register can be altered by re-exec uting the mode set command. All banks must
be in precharged 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 required. Low signals of RAS, CAS, and
WE at the positive edge of the clock activate the mode set operation. Address input data at this
timing defines parameters to be set as shown in the previous table.
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 selected bank is activated and all of sense
amplifi ers associated to the wordline ar e set. A CAS cycle is triggered b y 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 fas t access modes. In a single CAS cycle, serial data read or
write operations are allowed at up to a 143 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, and 8. Col umn addresses
are s egmented by the burst len gth and serial data ac cesses are done within this boundar y. The first
column address to be ac cessed is supplied at the CAS timi ng and the s ubsequent addresses are
generated automati call y by the programmed burst l ength and i ts sequenc e. F or ex ample, i n a burs t
length of 8 with int erl eave sequence, if the fir st add ress is ‘2’, then the rest of the burst se quence is
3, 0, 1, 6, 7, 4, and 5.
Similar to the page mode of conventional DRAM’s, burst read or write accesses on any column
address are possible once the RAS cycle latches the sense amplifiers. The maximum tRAS or the
refresh interval time limits the number of random column accesses. A new burst access can be