IBMN312164CT3
IBMN312804CT3
IBMN312404CT3
128Mb Synchronous DRAM - Die Revision B
Preliminary
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 man-
ner. During power on, all V
DD
and V
DDQ
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 V
DD
+0.3V on any of the
input pins or V
DD
supplies. The CK signal must be started at the same time. After power on, an initial pause of
200µs is required followed by a precharge of all banks using the precharge command. To prevent data con-
tention on the DQ bus during power on, it is required that the DQM and CKE pins be held high during the ini-
tial pause period. Once all banks have been precharged, the 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
For application flexibility, CAS latency, burst length, burst sequence, and operation type are user defined vari-
ables and must be programmed into the SDRAM Mode Register with a single Mode Register Set Command.
Any content of the Mode Register can be altered by re-executing the Mode Register Set Command. If the
user chooses to modify only a subset of the Mode Register variables, all four variables must be redefined
when the Mode Register Set Command is issued.
After initial power up, the Mode Register Set Command must be issued before read or write cycles may
begin. All banks must be in a precharged state and CKE must be high at least one cycle before the Mode
Register Set Command can be issued. The Mode Register Set Command is activated by the low signals of
RAS, CAS, CS, and WE at the positive edge of the clock. The address input data during this cycle defines the
parameters to be set as shown in the Mode Register Operation table. A new command may be issued follow-
ing the mode register set command once a delay equal to t
RSC
has elapsed.
CAS Latency
The CAS latency is a parameter that is used to define the delay from when a Read Command is registered on
a rising clock edge to when the data from that Read Command becomes available at the outputs. The CAS
latency is expressed in terms of clock cycles and can have a value of 2 or 3 cycles. The value of the CAS
latency is determined by the speed grade of the device and the clock frequency that is used in the application.
A table showing the relationship between the CAS latency, speed grade, and clock frequency appears in the
Electrical Characteristics section of this document. Once the appropriate CAS latency has been selected it
must be programmed into the mode register after power up, for an explanation of this procedure see Pro-
gramming the Mode Register in the previous section.
©IBM Corporation. All rights reserved.
Use is further subject to the provisions at the end of this document.
06K7582.H03335A
01/01
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