SDRAM
AS4SD4M16
Austin Semiconductor, Inc.
FUNCTIONAL DESCRIPTION
REGISTER DEFINITION
In general, the 64Mb SDRAM is quad-bank DRAM (1 Mode Register
Meg x 16 x 4 banks) which operate at 3.3V and include a The Mode Register is used to define the specific mode
synchronous interface (all signals are registered on the of operation of the SDRAM. This definition includes the
positive edge of the clock signal, CLK). Each of the x16’s selection of a burst length, a burst type, a CAS latency, an
16,777,216-bit banks is organized as 4,096 rows by 256 columns operating mode and a write burst mode, as shown in Figure 1.
by 16 bits.
The Mode Register is programmed via the LOAD MODE
Read and write accesses to the SDRAM are burst REGISTER command and will retain the stored information until
oriented; accesses start at a selected location and continue for it is programmed again or the device loses power.
a programmed number of locations in a programmed sequence.
Mode register bits M0-M2 specify the burst length,
Accesses begin with the registration of an ACTIVE command M3 specifies the type of burst (sequential or interleaved), M4-
which is then followed by a READ or WRITE command. The M6 specify the CAS latency, M7 and M8 specify the operating
address bits registered coincident with the ACTIVE command mode, M9 specifies the WRITE burst mode, and M10 and M11
are used to select the bank and row to be accessed (BA0 and are reserved for future use.
BA1 select the bank, A0-A11 select the row). The address bits
The Mode Register must be loaded when all banks are
( x16: A0-A7) registered coincident with the READ or WRITE idle, and the controller must wait the specified time before
command are used to select the starting column location for the initiating the subsequent operation. Violating either of these
burst access.
Prior to normal operation, the SDRAM must be initial-
ized. The following sections provide detailed information Burst Length
requirements will result in unspecified operation.
covering device initialization, register definition, command
descriptions and device operation.
Read and write accesses to the SDRAM are burst
oriented, with the burst length being programmable, as shown
in Figure 1. The burst length determines the maximum number
of column locations that can be accessed for a given READ or
WRITE command. Burst lengths of 1, 2, 4, or 8 locations are
available for both the sequential and the interleaved burst types,
and a full-page burst is available for the sequential type. The
full-page burst is used in conjunction with the BURST
TERMINATE command to generate arbitrary burst lengths.
Reserved states should not be used, as unknown
Initalization
SDRAMs must be powered up and initialized in a
predefined manner. Operational procedures other than those
specified may result in undefined operation. Once power is
applied to VDD and VDDQ (simultaneously) and the clock is
stable, the SDRAM requires a 100µs delay prior to applying an
executable command. Starting at some point during this 100µs
period and continuing at least through the end of this period,
COMMAND INHIBIT or NOP commands should be applied.
Once the 100µs delay has been satisfied with at least
one COMMAND INHIBIT or NOP command having been ap-
plied, a PRECHARGE command should be applied. All banks
must be precharged, thereby placing the device in the all banks
idle state.
Once in the idle state, two AUTO REFRESH cycles
must be performed. After the AUTO REFRESH cycles are
complete, the SDRAM is ready for Mode Register program-
ming. Because the Mode Register will power up in an unknown
state, it should be loaded prior to applying any operational
command.
operation or incompatibility with future versions may result.
When a READ or WRITE command is issued, a block
of columns equal to the burst length is effectively selected. All
accesses for that burst take place within this block, meaning
that the burst will wrap within the block if a boundary is reached.
The block is uniquely selected by A1-A7 (x16) when the burst
length is set to two; A2-A7 (x16) when the burst length is set to
four; and by A3-A7 (x16) when the burst length is set to eight.
The remaining (least significant) address bit(s) is (are) used to
select the starting location within the block. Full-page bursts
wrap within the page if the boundary is reached.
Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.
AS4SD4M16
Rev. 1.5 10/01
6
AUSTIN [ AUSTIN SEMICONDUCTOR ]
