MT48LC64M4A2_99 Datasheet, PDF (17/77 Pages) Micron Technology – Synchronous DRAM 256Mb: x4, x8, x16 SDRAM

256Mb: x4, x8, x16 SDRAM
Functional Description
Register Definition
Mode Register
The mode register is used to define the specific mode of operation of the SDRAM. This
definition includes the selection of BL, a burst type, CL, an operating mode, and a write
burst mode, as shown in Figure 7 on page 18. The mode register is programmed via the
LOAD MODE REGISTER command and will retain the stored information until it is
programmed again or the device loses power.
Mode register bits M0–M2 specify BL, M3 specifies the type of burst (sequential or inter-
leaved), M4–M6 specify CL, M7, and M8 specify the operating mode, M9 specifies the
write burst mode, and M10 and M11 are reserved for future use. Address A12 (M12) is
undefined but should be driven LOW during loading of the mode register.
The mode register must be loaded when all banks are idle, and the controller must wait
the specified time before initiating the subsequent operation. Violating either of these
requirements will result in unspecified operation.
Burst Length (BL)
Read and write accesses to the SDRAM are burst oriented, with BL being programmable,
as shown in Figure 7 on page 18. BL determines the maximum number of column loca-
tions 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 mode. The full-page burst is used in
conjunction with the BURST TERMINATE command to generate arbitrary BLs.
Reserved states cannot be used, because unknown operation or incompatibility with
future versions may result.
When a READ or WRITE command is issued, a block of columns equal to BL 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–
A9, A11 (x4), A1–A9 (x8) or A1–A8 (x16) when BL = 2; by A2–A9, A11 (x4), A2–A9 (x8) or
A2–A8 (x16) when BL = 4; and by A3–A9, A11 (x4), A3–A9 (x8) or A3–A8 (x16) when BL = 8.
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.
PDF: 09005aef8091e6d1/Source: 09005aef8091e6a8
256MSDRAM_2.fm - Rev. L 10/07 EN
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